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Compare quantitative distributions

Learning goals

  • Compares shape, center, spread, and unusual features across distributions.
  • Uses comparable graphical displays and numerical summaries.
  • Describes differences in context rather than only listing statistics.
  • Accounts for outliers or skew when choosing comparisons.

Click problems to add them to your worksheet.

Compare quantitative distributions 1
Group A has mean \(62\) and standard deviation \(5\). Group B has mean \(58\) and standard deviation \(2\). Compare typical level and consistency.

Hints

- Interpret center and spread as separate features. - A higher mean indicates a higher typical level under that summary; a smaller standard deviation indicates tighter clustering.

Solution

1. Group A has the higher mean, so its typical level is higher by \(4\). 2. Group B has the smaller standard deviation, so its values are more consistent around its mean.

Answer

Group A has the higher center; Group B has less variability and is more consistent.
Compare quantitative distributions 2
The dotplots show books borrowed by five students in each class. Which class has the higher median, a) or b)? Find both medians.
Figure for problem 563411

Hints

- Count how many observations are in each dotplot. - Find the middle dot after ordering the values in each group. - Compare those two middle values on the shared scale.

Solution

1. Each dotplot has five values. The median is the third value in order. 2. Class a)'s third value is \(3\); class b)'s is \(7\). 3. Class b) has the higher median.

Answer

Class b): median a) is \(3\) books and median b) is \(7\) books.
Compare quantitative distributions 3
Two pharmacy pickup options have recorded waiting times. Which has a wider middle \(50\%\) of waits: walk-in pickup or drive-through pickup?
Figure for problem 563412

Hints

- Which two boundaries enclose the central half of the data? - Both plots share a horizontal scale; compare the lengths of their central boxes.

Solution

1. The walk-in box extends from \(5\) to \(15\) minutes, giving an IQR of \(10\) minutes. 2. The drive-through box extends from \(8\) to \(12\) minutes, giving an IQR of \(4\) minutes. 3. Walk-in waits have the wider middle half.

Answer

Walk-in pickup, with an IQR of \(10\,\text{min}\), compared with \(4\,\text{min}\) for drive-through pickup.
Compare quantitative distributions 4
Both histograms use the same scale. Which distribution reaches across a wider stretch of the value axis? Name the first and last bins containing observations for each graph. Can you find either exact numerical range from these histograms?
Figure for problem 563520

Hints

- Find the farthest-left and farthest-right nonempty bars in each graph. - Compare those locations, not the number or heights of the bars. - Does a bin show the exact positions of the measurements inside it?

Solution

1. In a), all six observations are in the interval from \(20\) up to \(30\). 2. In b), the first occupied bin is \([0,10)\) and the last is \([40,50)\). 3. Thus b) covers a wider horizontal stretch. Neither exact range is known because the individual values within the bins are hidden.

Answer

Distribution b) covers a wider horizontal stretch. In a), both the first and last occupied bins are \([20,30)\). In b), they are \([0,10)\) and \([40,50)\). Exact ranges cannot be read from grouped data.
Compare quantitative distributions 5
Compare the centers and IQRs of distributions A and B.
Figure for problem 539759

Hints

- Read matching summary landmarks from both plots before comparing. - Compare medians for center and subtract \(Q_1\) from \(Q_3\) for each IQR.

Solution

1. The medians are \(24\) for A and \(28\) for B, so B has the higher center. 2. A has IQR \(30-18=12\). 3. B has IQR \(36-20=16\), so B has greater middle-half variability.

Answer

B has the higher median, \(28\) versus \(24\), and the larger IQR, \(16\) versus \(12\).
Compare quantitative distributions 6
The dotplots have the same median. Compare their spreads and shapes.
Figure for problem 539763

Hints

- Use the shared horizontal scale to compare the endpoints. - Compare how tightly the dots cluster around the common median. - Describe shape and spread separately.

Solution

1. Both medians are \(5\). 2. a) spans \(1\) to \(9\), while b) spans \(3\) to \(7\), so a) is more spread out. 3. Both are approximately symmetric and unimodal, but b) is more concentrated around the center.

Answer

Both are approximately symmetric with median \(5\); a) has greater spread, while b) is more concentrated.
Compare quantitative distributions 7
Which distribution has the larger IQR, and which has the larger range?
Figure for problem 539765

Hints

- Compute each spread measure separately; they can rank distributions differently. - Use the box width for IQR and the full endpoint distance for range; the measures need not agree.

Solution

1. A has IQR \(20-10=10\) and range \(40-0=40\). 2. B has IQR \(25-10=15\) and range \(30-5=25\). 3. B has the larger IQR, while A has the larger range.

Answer

Larger IQR: B, \(15\). Larger range: A, \(40\).
Compare quantitative distributions 8
Compare the likely skewness of A and B.
Figure for problem 539767

Hints

- Interpret the tail and median position in each boxplot separately. - Then compare the two inferred skew directions.

Solution

1. A has a much longer left whisker and a median closer to \(Q_3\), suggesting left skew. 2. B has a much longer right whisker, suggesting right skew.

Answer

A is likely left-skewed; B is likely right-skewed.
Compare quantitative distributions 9
Use the boxplots to compare \(Q_3\) of A with \(Q_1\) of B. What does this indicate about the middle halves?
Figure for problem 539768

Hints

- Compare the endpoints of the two boxes on the common scale. - Write each middle-half interval from \(Q_1\) to \(Q_3\), then find any common values.

Solution

1. For A, \(Q_3=40\). 2. For B, \(Q_1=35\). 3. Since \(35<40\), the middle \(50\%\) intervals \([20,40]\) and \([35,55]\) overlap from \(35\) to \(40\).

Answer

A’s \(Q_3=40\) exceeds B’s \(Q_1=35\), so the middle halves overlap on \([35,40]\).
Compare quantitative distributions 10
Two distributions have the same mean. Must they have the same shape and standard deviation? Explain.

Hints

- Consider how much information one summary statistic leaves unspecified. - Imagine rearranging observations around a fixed balance point while changing their distances from it.

Solution

1. The mean describes only one aspect of center. 2. Distributions can place observations differently around the same balance point. 3. Their shapes and standard deviations can therefore differ.

Answer

No. Equal means do not imply equal shape or variability.
Compare quantitative distributions 11
The boxplots show fill amounts in milliliters. Compare the medians and IQRs in context.
Figure for problem 539770

Hints

- Compare like landmarks and express differences with the variable’s units. - State both median differences and IQR differences in milliliters.

Solution

1. Machine A has median \(101\,\text{mL}\) and IQR \(104-98=6\,\text{mL}\). 2. Machine B has median \(102\,\text{mL}\) and IQR \(105-99=6\,\text{mL}\). 3. Machine B’s typical fill is \(1\,\text{mL}\) higher, while the middle-half variability is the same.

Answer

Machine B has a median \(1\,\text{mL}\) higher; both machines have IQR \(6\,\text{mL}\).
Compare quantitative distributions 12
Compare the modality and clustering in histograms a) and b).
Figure for problem 539771

Hints

- Locate the prominent peaks in each histogram. - Check whether a low-frequency or empty interval separates the peaks enough to form distinct clusters.

Solution

1. a) has one main peak near \(12.5\), so it is unimodal with one cluster. 2. b) has two separated peaks near \(7.5\) and \(37.5\), with a large central gap. 3. b) is bimodal with two distinct clusters.

Answer

a) is unimodal with one cluster; b) is bimodal with two clusters separated by a large gap.
Compare quantitative distributions 13
Two identical data sets are compared. In one set, the largest value is replaced by a much larger value. Which comparisons will show the greatest change: medians and IQRs, or means and standard deviations?

Hints

- Separate positional summaries from summaries that use every observation’s magnitude. - Decide which group of summaries is more sensitive to replacing one extreme value.

Solution

1. The replacement creates or enlarges a high extreme value. 2. Means and standard deviations are nonresistant and will change substantially. 3. Medians and IQRs are resistant and may change little or not at all.

Answer

The means and standard deviations will show the greatest change.
Compare quantitative distributions 14
Describe the relationship between the two distributions’ centers and spreads.
Figure for problem 539774

Hints

- Check whether corresponding landmarks differ by a constant. - A constant difference at every landmark signals a horizontal shift, while equal landmark gaps signal unchanged spread.

Solution

1. B’s five-number summary is exactly \(10\) greater at every landmark. 2. The medians differ by \(10\), but both IQRs are \(6\) and both ranges are \(12\). 3. B is a rightward shift of A with the same spread.

Answer

B is shifted \(10\) units higher than A, with the same IQR and range.
Compare quantitative distributions 15
Distribution B is created by adding \(7\) to every observation in distribution A. Compare the two distributions' shape, measures of center, and measures of spread.

Hints

- Track what happens to pairwise differences under a common shift. - Separate location summaries from spread summaries. - A translation preserves relative positions.

Solution

1. Adding \(7\) shifts every observation the same distance to the right. 2. The mean, median, quartiles, minimum, and maximum all increase by \(7\). 3. Differences between observations do not change, so the range, interquartile range, standard deviation, and shape remain unchanged.

Answer

B has the same shape and spread as A, while every measure of center and location is \(7\) units larger.
Compare quantitative distributions 16
Distribution B is created by multiplying every value in distribution A by \(2\). Distribution A has median \(12\), interquartile range \(3\), and range \(10\). Compare these summaries for A and B.

Hints

- Apply the scale factor to both values and distances. - Measures of spread are based on differences between values. - A positive scaling preserves ordering and shape.

Solution

1. Multiplying by \(2\) doubles every location value, so B's median is \(2\cdot12=24\). 2. All numerical distances double, so B's interquartile range is \(2\cdot3=6\). 3. B's range is \(2\cdot10=20\).

Answer

B has median \(24\), interquartile range \(6\), and range \(20\); each is twice the corresponding summary for A.
Compare quantitative distributions 17
Student A scored \(70\) on Test A and was at the \(80\)th percentile. Student B scored \(75\) on Test B and was at the \(60\)th percentile. Compare their raw scores and their relative standing within the two score distributions.

Hints

- Compare the numerical scores separately from the percentile ranks. - A percentile describes position relative to other scores on the same assessment. - Do not treat scores from different distributions as interchangeable measures of standing.

Solution

1. Student B has the higher raw score because \(75>70\). 2. Student A has the higher relative standing because the \(80\)th percentile exceeds the \(60\)th percentile. 3. Raw scores from different tests and percentile ranks answer different comparison questions.

Answer

Student B has the higher raw score, but Student A has the higher relative standing within the corresponding distribution.
Compare quantitative distributions 18
Every observation in both distributions A and B includes the same measurement offset of \(+5\). The offset is removed from both distributions. How do the difference between their means, their standard deviations, and their shapes change?

Hints

- Track the effect of the correction on each distribution separately. - Compare a difference of two quantities when both receive the same shift. - Location changes do not alter within-distribution distances.

Solution

1. Subtracting \(5\) from every value lowers each distribution's mean by \(5\). 2. Because both means change by the same amount, the difference between the means remains unchanged. 3. A common shift does not change either standard deviation or either shape.

Answer

The difference between the means, both standard deviations, and both shapes remain unchanged; each mean simply decreases by \(5\).
Compare quantitative distributions 19
Distribution A has mean \(0\) and standard deviation \(1\). Distribution B has mean \(2\) and standard deviation \(1\). What comparisons are supported by these summaries, and what cannot be determined about overlap and shape?

Hints

- State the direct center and spread comparisons first. - Ask which features require more than two numerical summaries. - Avoid assuming a normal model unless one is given.

Solution

1. B's mean is \(2\) units greater than A's, so B has the higher center by mean. 2. The equal standard deviations indicate equal variability by that measure. 3. Means and standard deviations alone do not determine distribution shape, outliers, or the exact amount of overlap. 4. Different pairs of distributions can share these summaries while having very different forms.

Answer

B has a mean \(2\) units higher, and the standard deviations are equal. Exact overlap and shape cannot be determined from these summaries alone.
Compare quantitative distributions 20
Distribution A has maximum \(40\). Distribution B has minimum \(45\). What can be concluded about every pair consisting of one observation from A and one from B?

Hints

- Use the most extreme value from each distribution. - Compare A's largest possible observation with B's smallest possible observation. - Nonoverlapping ranges support a statement about every cross-group pair.

Solution

1. Every observation in A is at most \(40\). 2. Every observation in B is at least \(45\). 3. Therefore every observation from B exceeds every observation from A by at least \(45-40=5\).

Answer

Every B observation is greater than every A observation, with a gap of at least \(5\).
Compare quantitative distributions 21
The dotplots show quiz-completion times, in minutes, for two classes. Compare the classes using shape, center, spread, and unusual features. Which class appears more consistent in completion time?
Figure for problem 556224

Hints

- Read each median from the ordered dots before comparing spread. - Compare both the overall horizontal span and the concentration around the center. - Look for asymmetry or isolated values that affect consistency.

Solution

1. Class A is approximately symmetric and concentrated around \(10\) minutes. Its median is \(10\), and its times range from \(8\) to \(12\) minutes. 2. Class B also has median \(10\), but it is right-skewed, with values extending from \(7\) to \(17\) minutes and a separated high value at \(17\). 3. Because the centers by median are the same, the main difference is spread and shape. 4. Class A has a much narrower range and stronger concentration near the center, so Class A is more consistent.

Answer

Both classes have median \(10\) minutes. Class A is approximately symmetric and tightly clustered from \(8\) to \(12\) minutes. Class B is right-skewed, spreads from \(7\) to \(17\) minutes, and has a separated high value at \(17\). Class A is more consistent.
Compare quantitative distributions 22
A courier recorded delivery times of \(18,19,20,21,22\) minutes on the Downtown route and \(10,15,20,25,30\) minutes on the Riverside route. Find each mean and range. Which route had more variable delivery times?

Hints

- Compare the totals and the number of observations before finding the means. - The range runs from the minimum to the maximum in each group. - Equal means do not force the distributions to have the same spread.

Solution

1. Each set totals \(100\) minutes for five deliveries, so both means are \(20\) minutes. 2. The Downtown range is \(22-18=4\) minutes; the Riverside range is \(30-10=20\) minutes. 3. Riverside delivery times vary more despite having the same mean.

Answer

Both means are \(20\) minutes. Downtown range: \(4\) minutes. Riverside range: \(20\) minutes. Riverside delivery times vary more.
Compare quantitative distributions 23
Which distribution has the same center but less variability? Support the answer with two measures of spread.
Figure for problem 539760

Hints

- Compare the medians to verify whether the centers match. - Compare the box widths to evaluate the IQRs. - Compare the full endpoint spans as a second measure of variability.

Solution

1. Both medians are \(12\). 2. Morning has IQR \(17-8=9\) and range \(25-4=21\). 3. Evening has IQR \(14-10=4\) and range \(20-5=15\). 4. Evening has less variability.

Answer

Evening; both medians are \(12\), but its IQR is \(4\) versus \(9\), and its range is \(15\) versus \(21\).
Compare quantitative distributions 24
Compare the shapes of histograms a) and b). Then use the midpoint of each bin to estimate the mean of each distribution and compare the estimated centers.
Figure for problem 539761

Hints

- Describe each histogram's shape before comparing centers. - Treat each bin midpoint as the representative value for observations in that bin. - Weight each midpoint by its displayed frequency.

Solution

1. Histogram a) is approximately symmetric, while histogram b) is skewed right. 2. For a), the midpoint estimate is \(\frac{2(5)+6(15)+12(25)+6(35)+2(45)}{28}=25\). 3. For b), the midpoint estimate is \(\frac{10(5)+8(15)+5(25)+3(35)+2(45)}{28}=17.5\). 4. Histogram a) therefore has the higher estimated mean by \(25-17.5=7.5\) units.

Answer

a) is approximately symmetric; b) is right-skewed. The midpoint mean estimates are \(25\) for a) and \(17.5\) for b), so a) has the higher estimated mean by \(7.5\) units.
Compare quantitative distributions 25
A planner claims Route X is always faster because its median is lower. Evaluate the claim using the boxplots.
Figure for problem 539762

Hints

- Distinguish a statement about typical values from a statement about every observation. - Translate “always faster” into a claim about every pair of trips. - Use overlap and unusual points to test that universal claim.

Solution

1. Route X has a lower median, \(30\) minutes versus \(35\) minutes. 2. However, the distributions overlap substantially, and Route X has a high outlier at \(50\) minutes. 3. A lower median does not imply every Route X trip is faster than every Route Y trip.

Answer

The claim is false. Route X has a lower median, but the distributions overlap and Route X includes a high outlier at \(50\) minutes.
Compare quantitative distributions 26
A teacher claims group a) has a higher median and less variability than group b). Is the claim supported by the dotplots?
Figure for problem 539766

Hints

- Read the ordered observations from each dotplot to locate the middle positions. - Compare the full horizontal extent of the two distributions. - Evaluate the center claim and variability claim separately.

Solution

1. Group a) has median \(3.5\), while group b) has median \(3\), so a) has a slightly higher center. 2. Group a) ranges from \(2\) to \(6\), while group b) ranges from \(1\) to \(8\). 3. Group b) is visibly more spread out, so the variability part of the claim is also supported.

Answer

Yes. Group a) has a slightly higher median and a much smaller spread.
Compare quantitative distributions 27
Lucía claims, “Nearly all values in distribution A are lower than nearly all values in distribution B.” Evaluate the claim using only the boxplots.
Figure for problem 539773

Hints

- Read the upper quartile of A and lower quartile of B from the plots. - Translate those quartiles into statements about broad portions of each distribution. - Check whether the corresponding value intervals overlap.

Solution

1. From the boxplots, A has \(Q_3=30\) and B has \(Q_1=25\). 2. Approximately \(75\%\) of A is at or below \(30\), while approximately \(75\%\) of B is at or above \(25\). 3. Because \(25<30\), these broad portions can overlap from \(25\) to \(30\). 4. The boxplots therefore do not establish the claimed near-complete ordering.

Answer

The claim is not established. A's \(Q_3=30\) exceeds B's \(Q_1=25\), so the distributions can overlap from \(25\) to \(30\).
Compare quantitative distributions 28
The groups have different sample sizes, but the charts use relative frequencies. Compare their centers and shapes without using counts.
Figure for problem 539775

Hints

- Use the relative-frequency scales to compare the panels directly despite different sample sizes. - Locate the main concentration to compare centers. - Inspect which side tapers farther to compare shapes.

Solution

1. a) is symmetric and centered in the middle interval. 2. b) places more relative frequency in higher intervals and has a longer lower-value side. 3. b) has a higher center and is somewhat left-skewed compared with a).

Answer

a) is symmetric with a lower center; b) has a higher center and is somewhat left-skewed.
Compare quantitative distributions 29
Compare the two distributions with respect to center, middle spread, and unusual values.
Figure for problem 539776

Hints

- Compare the median lines for center. - Compare the box widths for middle-half spread. - Inspect points beyond the whiskers separately from the box comparison.

Solution

1. Both medians are \(20\). 2. A has IQR \(25-15=10\), while B has IQR \(30-10=20\). 3. A has two high outliers at \(40\) and \(45\); B has none displayed. 4. B has a wider middle half, while A has more extreme unusual values.

Answer

Same median \(20\); B has larger IQR \(20\) versus \(10\); A has high outliers at \(40\) and \(45\).
Compare quantitative distributions 30
Which distribution is likely to have the larger difference between mean and median? Explain.
Figure for problem 539777

Hints

- Identify the direction and strength of asymmetry in each plot. - Recall that the mean is pulled toward a long tail. - Use the stronger asymmetry to predict which mean–median gap is larger.

Solution

1. A has a pronounced long right whisker, indicating stronger right skew. 2. Right skew tends to pull the mean above the median. 3. B is more nearly symmetric, so its mean and median are likely closer. 4. A likely has the larger difference.

Answer

Distribution A, because its stronger right skew is likely to pull the mean farther above the median.
Compare quantitative distributions 31
The dotplots show distributions A and B. Both have mean \(10\) and range \(20\). Which distribution has the larger standard deviation? Explain using distances from the common mean rather than the range alone.
Figure for problem 539778

Hints

- Equal ranges do not imply equal standard deviations. - Compare how far most observations lie from the shared mean. - Standard deviation increases when more observations are concentrated farther from the center.

Solution

1. Both distributions have the same center and the same range, so those facts alone do not decide the comparison. 2. In A, four of the six observations lie within \(1\) unit of the mean, while only the two endpoints are \(10\) units away. 3. In B, every observation is \(10\) units from the mean. 4. Because B has much larger typical squared distances from the common mean, B has the larger standard deviation.

Answer

Distribution B has the larger standard deviation because all of its observations lie far from the common mean, whereas most of A is concentrated near the mean.
Compare quantitative distributions 32
The ogive compares cumulative relative frequencies for distributions A and B. Lower values are preferable. Compare the distributions at thresholds \(10\), \(20\), and \(30\). Identify the interval containing each median and state which distribution generally tends to have lower values.
Figure for problem 548811

Hints

- Read an ogive height as the cumulative proportion at or below that x-value. - Locate where each curve first crosses the \(0.50\) level. - Compare the two curves at the same threshold.

Solution

1. Reading the ogive, B has the larger cumulative relative frequency at each listed threshold below \(40\). 2. A is at \(0.35\) by \(20\) and \(0.75\) by \(30\), so A's median lies in \((20,30]\). 3. B is at \(0.20\) by \(10\) and \(0.60\) by \(20\), so B's median lies in \((10,20]\). 4. The consistently larger cumulative proportions for B indicate that B generally has lower values across these thresholds.

Answer

A's median lies in \((20,30]\), and B's median lies in \((10,20]\). Distribution B generally tends lower because a larger proportion of B is at or below each listed threshold.
Compare quantitative distributions 33
The back-to-back stem-and-leaf plot compares distributions A and B. A key is \(1\mid2=12\). <table><thead><tr><th>A leaves</th><th>Stem</th><th>B leaves</th></tr></thead><tbody><tr><td>\(8\ 5\ 4\ 2\)</td><td>\(1\)</td><td>\(8\ 9\)</td></tr><tr><td>\(8\ 5\ 3\ 1\)</td><td>\(2\)</td><td>\(2\ 4\ 7\ 9\)</td></tr><tr><td></td><td>\(3\)</td><td>\(1\ 3\)</td></tr></tbody></table> Compare the medians, interquartile ranges, and overall locations of the two distributions.

Hints

- Read the left leaves in the correct order for distribution A. - Reconstruct each ordered list before locating quartiles. - Compare location and spread as separate features.

Solution

1. A is \(12,14,15,18,21,23,25,28\), with median \(\frac{18+21}{2}=19.5\). 2. B is \(18,19,22,24,27,29,31,33\), with median \(\frac{24+27}{2}=25.5\). 3. For A, \(Q_1=\frac{14+15}{2}=14.5\) and \(Q_3=\frac{23+25}{2}=24\), so \(\text{IQR}=9.5\). 4. For B, \(Q_1=\frac{19+22}{2}=20.5\) and \(Q_3=\frac{29+31}{2}=30\), so \(\text{IQR}=9.5\). 5. B is shifted toward higher values while the middle-half spreads are equal.

Answer

A has median \(19.5\) and IQR \(9.5\). B has median \(25.5\) and IQR \(9.5\). B is generally located higher, with the same middle-half variability.
Compare quantitative distributions 34
Use the two dotplots to compare centers, ranges, and shapes. Explain why matching numerical summaries do not make the distributions equivalent.
Figure for problem 548813

Hints

- Read each set of observations from its dotplot before computing summaries. - Compare where observations are concentrated within the common range. - A few numerical summaries do not encode the full shape.

Solution

1. Reading the dotplots, A is \(0,0,5,10,10\) and B is \(0,4,5,6,10\). 2. Both distributions have mean \(5\), median \(5\), and range \(10\). 3. A is concentrated at the two ends with a middle value, while B is concentrated near \(5\) and tapers toward the endpoints. 4. Equal center and range do not determine a distribution's shape or concentration.

Answer

Both distributions have mean \(5\), median \(5\), and range \(10\), but A is concentrated at the ends while B is concentrated near the center.
Compare quantitative distributions 35
Two distributions have the following percentile profiles. <table><thead><tr><th>Percentile</th><th>A</th><th>B</th></tr></thead><tbody><tr><td>\(10\)th</td><td>\(5\)</td><td>\(5\)</td></tr><tr><td>\(25\)th</td><td>\(12\)</td><td>\(8\)</td></tr><tr><td>\(50\)th</td><td>\(20\)</td><td>\(20\)</td></tr><tr><td>\(75\)th</td><td>\(28\)</td><td>\(32\)</td></tr><tr><td>\(90\)th</td><td>\(35\)</td><td>\(35\)</td></tr></tbody></table> Compare the center, the spread of the middle \(50\%\), and the spread in the two outer percentile bands from the \(10\)th to \(25\)th and from the \(75\)th to \(90\)th percentiles.

Hints

- Use matching percentile positions to define comparable intervals. - Separate the middle-half width from the two outer-band widths. - Equal endpoints at the \(10\)th and \(90\)th percentiles do not force equal internal spread.

Solution

1. Both medians are \(20\). 2. A has \(\text{IQR}=28-12=16\), while B has \(\text{IQR}=32-8=24\). B is more spread out in the middle \(50\%\). 3. For A, each outer percentile band has width \(12-5=7\) and \(35-28=7\). 4. For B, each outer percentile band has width \(8-5=3\) and \(35-32=3\). 5. A has more spread in the outer bands, while B has more spread in the middle half.

Answer

Both medians are \(20\). B has the larger IQR, \(24\) versus \(16\). A has wider outer percentile bands, \(7\) units each versus \(3\) units each for B.
Compare quantitative distributions 36
Six concertgoers waited for rides. The dotplot gives their recorded waiting times. One wait recorded as \(18\) minutes was actually \(100\) minutes. Compare the mean, median, range, and IQR of the recorded and actual waits. Round the means to two decimal places. Which summaries stay the same?
Figure for problem 548817

Hints

- Read each plotted dot as one wait, including the stack at the largest recorded time. - How does correcting one wait change the ordered list? - Check the measures based on middle positions separately from those involving all values or the extremes.

Solution

1. The recorded waits are \(10,12,14,16,18,18\). The actual waits are \(10,12,14,16,18,100\). 2. The recorded mean is \(\frac{88}{6}\approx14.67\) minutes; the actual mean is \(\frac{170}{6}\approx28.33\) minutes. 3. Both medians are \(\frac{14+16}{2}=15\). 4. The recorded range is \(18-10=8\) minutes; the actual range is \(100-10=90\) minutes. 5. For both, \(Q_1=12\) and \(Q_3=18\), so \(\text{IQR}=6\). 6. The median and IQR stay the same; the mean and range change.

Answer

Recorded: mean \(14.67\) minutes, median \(15\) minutes, range \(8\) minutes, IQR \(6\) minutes. Actual: mean \(28.33\) minutes, median \(15\) minutes, range \(90\) minutes, IQR \(6\) minutes. Unchanged: median and IQR.
Compare quantitative distributions 37
The ordered values of distribution A are \(10,20,30,40,50\), and the ordered values of distribution B are \(12,19,35,44,60\). Pair observations with the same rank and calculate \(B-A\) at each rank. Is B a constant translation of A? Find the median rank-by-rank difference and describe how the separation changes across the distributions.

Hints

- Match smallest with smallest, second-smallest with second-smallest, and so on. - A pure translation would produce the same difference at every rank. - Summarize the set of rank differences after calculating all of them.

Solution

1. The rank-by-rank differences are \(12-10=2\), \(19-20=-1\), \(35-30=5\), \(44-40=4\), and \(60-50=10\). 2. The differences are not constant, so B is not a translation of A. 3. In order, the differences are \(-1,2,4,5,10\), so their median is \(4\). 4. The upper end of B is farther above A than the lower end, while B's second ordered value is slightly below A's.

Answer

The rank differences are \(2,-1,5,4,10\), with median \(4\). B is not a constant translation of A because the differences vary, especially at the upper end.
Compare quantitative distributions 38
Distribution A has \(5\)th percentile \(40\), median \(50\), and \(95\)th percentile \(60\). Distribution B has \(5\)th percentile \(35\), median \(50\), and \(95\)th percentile \(65\). Compare the typical values and the widths of the central \(90\%\) intervals. State one feature that cannot be determined from these three percentiles alone.

Hints

- Compare matching percentile locations across the two distributions. - Subtract the lower percentile from the upper percentile to measure the stated central interval. - Distinguish information supplied by selected percentiles from information requiring the full distribution.

Solution

1. Both medians are \(50\), so their typical values by median are equal. 2. A's central \(90\%\) interval has width \(60-40=20\). 3. B's central \(90\%\) interval has width \(65-35=30\). 4. B has greater spread across its central \(90\%\). 5. The three percentiles do not determine features such as exact shape, standard deviation, sample size, or the most extreme values.

Answer

Both medians are \(50\). The central \(90\%\) widths are \(20\) for A and \(30\) for B, so B is more spread out over that percentile interval. Exact shape or standard deviation cannot be determined.
Compare quantitative distributions 39
A pool test measures chlorine in parts per million (ppm). For readings below \(2\,\text{ppm}\), its software records \(2\,\text{ppm}\); other readings stay the same. The dotplots show true levels (A) and stored levels (B). Compare their means, medians, ranges, and shapes. How does the recording rule change the picture?
Figure for problem 548821

Hints

- Apply the stated recording rule to the smallest actual observations. - Read both dotplots as numerical lists before computing the summaries. - Distinguish a stack created by recording from a real cluster of equal values.

Solution

1. A has values \(0,1,2,3,4,5\), with mean \(2.5\), median \(2.5\), and range \(5\). 2. B has recorded values \(2,2,2,3,4,5\), with mean \(3\), median \(2.5\), and range \(3\). 3. A has one observation at each value from \(0\) through \(5\), while B has three recorded at \(2\). 4. The rule raises the recorded mean, leaves the median unchanged here, reduces the range, and creates an artificial stack at \(2\).

Answer

A: mean \(2.5\,\text{ppm}\), median \(2.5\,\text{ppm}\), range \(5\,\text{ppm}\), evenly spaced. B: mean \(3\,\text{ppm}\), median \(2.5\,\text{ppm}\), range \(3\,\text{ppm}\), with a stack at \(2\,\text{ppm}\). Recording small values as \(2\) distorts the mean, range, and visible shape.
Compare quantitative distributions 40
The dotplots show distributions A and B together with the common target value \(55\). Compare the two distributions' ordinary variability and their average absolute distance from the target. Which distribution is more tightly centered on the target?
Figure for problem 548823

Hints

- Read the observations from each plot and compare their internal spacing. - Then measure each observation's distance from the dashed target line. - Internal variability and closeness to an external target are different comparisons.

Solution

1. Reading the plots, A is \(48,50,52,54\) and B is \(52,54,56,58\). B is obtained by adding \(4\) to every value in A, so the two distributions have the same range and standard deviation. 2. A's absolute distances from \(55\) are \(7,5,3,1\), with mean distance \(4\). 3. B's absolute distances from \(55\) are \(3,1,1,3\), with mean distance \(2\). 4. The distributions have equal internal spread, but B is more tightly centered on the external target.

Answer

A and B have equal ordinary variability. Their average absolute distances from \(55\) are \(4\) and \(2\), respectively, so B is more tightly centered on the target.
Compare quantitative distributions 41
Distribution A is approximately symmetric and is summarized by mean \(40\) and standard deviation \(6\). Distribution B is right-skewed and is summarized by median \(40\) and interquartile range \(9\). Can you determine which distribution is more variable from these summaries alone? Explain.

Hints

- Identify which spread statistic is used for each distribution. - Ask whether the two numbers measure the same feature in the same way. - A valid comparison requires a common metric or more information.

Solution

1. A's spread is reported with standard deviation, while B's spread is reported with interquartile range. 2. These measures describe different aspects of variability and have different numerical scales. 3. Without a common spread measure or additional distribution information, \(6\) and \(9\) cannot be compared directly to determine which distribution is more variable.

Answer

No. Standard deviation \(6\) and interquartile range \(9\) are not directly comparable measures of spread.
Compare quantitative distributions 42
In distribution A, \(Q_3=70\). In distribution B, the median is \(70\). Compare the proportions at or above \(70\) that these summary positions suggest. Explain why ties at \(70\) prevent an exact comparison.

Hints

- Translate each summary position into an approximate percentile statement first. - Distinguish observations strictly above \(70\) from observations equal to \(70\). - Test whether repeated values at the threshold could change the at-or-above proportions.

Solution

1. As a quartile-position interpretation, \(Q_3=70\) suggests that about the upper \(25\%\) of A is at or above \(70\). 2. A median of \(70\) suggests that about \(50\%\) of B is at or above \(70\). 3. These percentages are exact only under additional assumptions about the data and the percentile convention. Repeated observations at \(70\) can make the proportion at or above \(70\) larger. 4. Therefore the summary positions suggest a larger share for B when there are no relevant ties, but the exact shares—and even which at-or-above share is larger—cannot be determined from the two summary values alone.

Answer

Without relevant ties, the quartile positions suggest about \(25\%\) of A and \(50\%\) of B at or above \(70\). With ties at \(70\), the exact proportions may be larger, so the two shares cannot be ordered with certainty from the given information alone.
Compare quantitative distributions 43
Two distributions with positive standard deviations are each standardized by subtracting their own mean and dividing by their own standard deviation. What center and spread will the standardized distributions share? Which features can still differ?

Hints

- Recall what the two parts of standardization do to location and scale. - A linear transformation does not rearrange observations. - Equal center and spread do not determine shape.

Solution

1. Standardization makes each transformed distribution have mean \(0\). 2. It makes each transformed distribution have standard deviation \(1\). 3. The transformation is linear with a positive scale factor, so each distribution keeps its own shape, skewness, clusters, gaps, and outlier pattern in standardized units. 4. Therefore two standardized distributions can share center and spread while still having different shapes.

Answer

Both standardized distributions have mean \(0\) and standard deviation \(1\), but their shapes and unusual features can still differ.
Compare quantitative distributions 44
The two boxplots have the same quartiles and median but different lower whiskers. Compare their center, middle spread, and likely shape.
Figure for problem 548828

Hints

- Compare the common box before inspecting the whiskers. - Measure tail lengths on both sides of each box. - Equal center and middle spread do not imply equal shape.

Solution

1. Both distributions have median \(15\) and interquartile range \(20-10=10\). 2. A has whiskers of lengths \(10-0=10\) and \(25-20=5\), so it is only mildly longer on the left. 3. B has a much longer lower whisker, \(10-(-20)=30\), and upper whisker length \(5\). 4. B's boxplot suggests much stronger left skew, even though the two distributions share the same median and interquartile range.

Answer

Both medians are \(15\), and both interquartile ranges are \(10\). B has much greater lower-tail spread, and its boxplot suggests stronger left skew.
Compare quantitative distributions 45
Two delivery services tracked delivery times in minutes. Cedar's interquartile interval is \([10, 30]\), and Harbor's is \([22, 40]\). Find the interval where their middle-half ranges overlap and its length. What percentage of each service's IQR length does this overlap cover? Round percentages to two decimal places. Explain why these are not percentages of deliveries with identical times.

Hints

- Which values fall inside both middle-half intervals? - Use each service's own interquartile range when finding a percentage. - What extra information about individual delivery times would be needed to count matching times?

Solution

1. The common interval is \([22, 30]\), with length \(30-22=8\) minutes. 2. Cedar's IQR length is \(30-10=20\) minutes, so the overlap is \(\frac{8}{20}\cdot100\%=40.00\%\) of that length. 3. Harbor's IQR length is \(40-22=18\) minutes, so the overlap is \(\frac{8}{18}\cdot100\%\approx44.44\%\) of that length. 4. These percentages compare lengths of intervals, not counts of deliveries. The intervals alone cannot tell how many deliveries took identical amounts of time.

Answer

Overlap: \([22, 30]\), length \(8\) minutes. This is \(40.00\%\) of Cedar's IQR length and \(44.44\%\) of Harbor's IQR length. The percentages compare interval lengths, not the share of deliveries with identical times.
Compare quantitative distributions 46
Distribution A has minimum \(0\) and maximum \(10\). Distribution B has minimum \(8\) and maximum \(20\). a) Identify the interval in which observations from the two distributions could overlap. b) Is every observation from B necessarily greater than every observation from A? c) State the guaranteed comparisons for any A-value below \(8\) and any B-value above \(10\).

Hints

- Treat each minimum-to-maximum span as an interval of possible values. - Find the intersection of the two intervals. - Use each distribution's extreme value to make guaranteed comparisons outside the overlap.

Solution

1. A occupies values from \(0\) through \(10\), and B occupies values from \(8\) through \(20\), so possible overlap is from \(8\) through \(10\). 2. It is not guaranteed that every B-value exceeds every A-value because both distributions may contain values in the overlap interval. 3. Any A-value below \(8\) is less than every B-value, since B's minimum is \(8\). 4. Any B-value above \(10\) is greater than every A-value, since A's maximum is \(10\).

Answer

a) Possible overlap: \([8,10]\) b) No. c) Every A-value below \(8\) is below all B-values, and every B-value above \(10\) is above all A-values.
Compare quantitative distributions 47
Distribution A is measured in degrees Fahrenheit and has mean \(68\) and standard deviation \(9\). Distribution B is measured in degrees Celsius and has mean \(22\) and standard deviation \(4\). Convert B's summaries to degrees Fahrenheit and compare the distributions' centers and spreads.

Hints

- Convert both summaries to one common unit before comparing. - The additive part of a linear conversion affects center but not spread. - Compare center and variability separately.

Solution

1. B's mean in degrees Fahrenheit is \(1.8\cdot22+32=71.6\). 2. B's standard deviation is multiplied only by \(1.8\), giving \(1.8\cdot4=7.2\). 3. B has the higher mean by \(71.6-68=3.6\) degrees Fahrenheit. 4. B has the smaller standard deviation, \(7.2\) versus \(9\), so it is less variable.

Answer

B has mean \(71.6^\circ\text{F}\) and standard deviation \(7.2^\circ\text{F}\). B has the higher center and smaller spread.
Compare quantitative distributions 48
Distribution A has mean \(5\), standard deviation \(3\), and is right-skewed. Distribution B is formed by replacing every value \(x\) with \(-2x\). Compare B's mean, standard deviation, and shape with A's.

Hints

- Apply the signed scale factor to the center. - Use the magnitude of the factor for spread. - A negative factor reverses left and right.

Solution

1. B's mean is \(-2\cdot5=-10\). 2. Multiplying by \(-2\) multiplies distances by \(2\), so B's standard deviation is \(2\cdot3=6\). 3. The negative factor reflects the distribution, so A's right skew becomes left skew in B.

Answer

B has mean \(-10\), standard deviation \(6\), and is left-skewed.
Compare quantitative distributions 49
Distribution A is \(10,20,30,40,50\), and distribution B is \(100,101,102,103,1000\). Within each distribution, replace each observation by its percentile rank using \(100\cdot\frac{\text{rank}}{5}\). Compare the two percentile-rank distributions and explain what information this transformation preserves and loses.

Hints

- Assign ranks separately within each distribution. - Apply the stated rank-to-percentile rule to each ordered position. - Compare what rank records with what raw numerical differences record.

Solution

1. Each distribution has five distinct ordered observations with ranks \(1,2,3,4,5\). 2. Both percentile-rank distributions are \(20,40,60,80,100\). 3. The transformation preserves the within-distribution order and relative rank of each observation. 4. It removes the original units and numerical distances. In particular, B's extreme gap from \(103\) to \(1000\) is no longer visible.

Answer

Both transformed distributions are \(20,40,60,80,100\). Percentile ranks preserve order and relative standing but discard original units, spacing, and magnitude of gaps.
Compare quantitative distributions 50
The histograms show travel times, in minutes, for two bus routes during the same time period. Compare Route A and Route B in context using shape, center, spread, and unusual features. Then state which route appears to have the lower typical travel time and which appears more predictable.
Figure for problem 556223

Hints

- Compare the two shapes before comparing centers. - Use the common horizontal scale to judge where most trips fall and how far each distribution extends. - Separate “typically faster” from “more consistent.”

Solution

1. Route A is approximately symmetric and unimodal, with its highest frequency in the \([20,25)\)-minute interval and most trips between about \(15\) and \(30\) minutes. 2. Route B is right-skewed: most trips are in the lower intervals, with a tail extending toward \(40\) minutes. 3. Route B has the lower typical travel time because much of its distribution lies below Route A's center. 4. Route A occupies a narrower effective span, about \(10\) to \(35\) minutes, while Route B extends from about \(5\) to \(40\) minutes and has the longer right tail. 5. Neither histogram shows an interior gap. Route A therefore appears more predictable, while Route B is typically faster but more variable.

Answer

Route A is approximately symmetric and unimodal, centered around the low \(20\)s, with a narrower spread. Route B is right-skewed, centered lower, and extends across a wider range with a long high-time tail. Route B appears to have the lower typical travel time, while Route A appears more predictable.
Compare quantitative distributions 51
Two school shuttles recorded trip times in minutes. East shuttle: \(12,14,16,18,20,22\). West shuttle: \(13,14,15,16,19,44\). Find the mean and median for each shuttle. Which shuttle has the shorter typical trip by median, and why does comparing only means tell a different story?

Hints

- Calculate the average of each list, then locate the two middle values. - Do the mean and median rank the shuttles the same way? - Which single value has an unusually large effect on one mean?

Solution

1. East mean is \(\frac{102}{6}=17\) minutes and median is \(\frac{16+18}{2}=17\) minutes. 2. West mean is \(\frac{121}{6}\approx20.17\) minutes, while median is \(\frac{15+16}{2}=15.5\) minutes. 3. West has the shorter median trip, but its unusually long \(44\)-minute trip raises its mean above East's.

Answer

East: mean \(17\) minutes, median \(17\) minutes. West: mean about \(20.17\) minutes, median \(15.5\) minutes. West has the shorter median; its \(44\)-minute trip makes its mean higher.
Compare quantitative distributions 52
Distribution B is formed by squaring every value in distribution A shown in the dotplots. Compare the medians, interquartile ranges, ranges, and shapes of A and B. Explain why this transformation behaves differently from a positive linear rescaling.
Figure for problem 548816

Hints

- Read A from the first dotplot and check how squaring changes each position. - Reorder the transformed values before finding quartiles. - Compare whether different A-values map to the same B-value.

Solution

1. From the dotplots, A is \(-3,-2,-1,0,1,2,3\), so its median is \(0\), \(Q_1=-2\), \(Q_3=2\), \(\text{IQR}=4\), and range is \(6\). 2. B in order is \(0,1,1,4,4,9,9\), so its median is \(4\), \(Q_1=1\), \(Q_3=9\), \(\text{IQR}=8\), and range is \(9\). 3. A is symmetric, while B is concentrated near the lower end with a right tail toward \(9\). 4. Squaring is not one-to-one across negative and positive values and is not increasing over all real numbers, so it can merge observations and change order and shape.

Answer

A: median \(0\), IQR \(4\), range \(6\), symmetric. B: median \(4\), IQR \(8\), range \(9\), right-skewed. Squaring merges opposite values and changes order, so it is not a simple positive rescaling.
Compare quantitative distributions 53
Use the dotplots to show that both groups have the same mean and sample standard deviation, but different interquartile ranges. Use the median-of-halves convention. Round standard deviations to three decimal places. What does the result show about comparing spread?
Figure for problem 548827

Hints

- Read and order the values from each plot. - Compare the totals and squared totals before doing separate variance calculations. - For quartiles, find the medians of the lower and upper halves separately.

Solution

1. Read A as \(0,0,0,3,3\) and B as \(0,0,1,1,4\). 2. Both lists have sum \(6\) and sum of squares \(18\), so the mean is \(1.2\) and the sample variance is \(\frac{18-5(1.2)^2}{4}=2.7\). 3. Both sample standard deviations are \(\sqrt{2.7}\approx1.643\). 4. A has \(Q_1=0\), \(Q_3=3\), and IQR \(3\). B has \(Q_1=0\), \(Q_3=2.5\), and IQR \(2.5\). 5. Equal standard deviations do not guarantee equal IQRs.

Answer

Both means are \(1.2\); both sample standard deviations are approximately \(1.643\). IQR A is \(3\); IQR B is \(2.5\). Different measures of spread can differ even when another agrees.
Compare quantitative distributions 54
One observation is selected at random from each of the two displayed distributions. Find the proportion of the \(9\) possible A–B pairs for which the B observation is greater than the A observation. Compare this result with the two medians.
Figure for problem 548837

Hints

- Read the three values in each distribution from the dotplots. - Treat each cross-group pairing as one equally likely outcome. - Compare the pairwise result with, rather than replacing it by, the median comparison.

Solution

1. From the dotplots, A is \(1,4,5\) with median \(4\), and B is \(2,3,6\) with median \(3\). 2. If B contributes \(2\), it exceeds only A's \(1\), giving \(1\) favorable pair. 3. If B contributes \(3\), it again exceeds only A's \(1\), giving \(1\) favorable pair. 4. If B contributes \(6\), it exceeds all three A-values, giving \(3\) favorable pairs. 5. Thus B exceeds A in \(5\) of the \(9\) pairs, or \(\frac{5}{9}\), even though B's median is lower.

Answer

The proportion is \(\frac{5}{9}\). A has median \(4\), while B has median \(3\), so the median comparison and the all-pairs comparison point in different directions.
Compare quantitative distributions 55
Distribution B is formed by rounding every value in A to the nearest multiple of \(10\), as shown in the dotplots. Compare the means, medians, ranges, interquartile ranges, and visible effects of rounding.
Figure for problem 548838

Hints

- Read both displayed data sets before calculating summaries. - Recalculate the rounded distribution instead of assuming every measure gets smaller. - Compare endpoints and quartile positions separately.

Solution

1. Reading the plots, A is \(14,16,24,26,34,36\), while B is \(10,20,20,30,30,40\). 2. Both distributions have sum \(150\), so both means are \(25\). Both medians are also \(25\). 3. A's range is \(22\), while B's range is \(30\). 4. For A, \(Q_1=16\) and \(Q_3=34\), so \(\text{IQR}=18\). For B, \(Q_1=20\) and \(Q_3=30\), so \(\text{IQR}=10\). 5. Rounding creates ties, leaves both centers unchanged here, increases the range, and decreases the IQR.

Answer

Both means and medians are \(25\). A has range \(22\) and IQR \(18\); B has range \(30\) and IQR \(10\). Rounding creates ties and can change different spread measures in different directions.

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