A survey asked \(200\) students how many minutes their trip to school takes. The histogram shows the relative frequencies in \(10\)-minute intervals.
a) State the relative frequency for each of the five intervals.
b) How many students have a travel time from \(10\) to \(20\) minutes?
c) Estimate the mean travel time. Use each interval midpoint, such as \(5\) minutes for the interval from \(0\) to \(10\) minutes.

Hints
- Read each bar height as a percent.
- Multiply the relative frequency by the total number of students to find a count.
- For the estimated mean, multiply each interval midpoint by its relative frequency written as a decimal, then add the products.
- Find the number halfway between the endpoints of each interval.
Solution
1. The relative frequencies are \(20\%\), \(35\%\), \(25\%\), \(15\%\), and \(5\%\) for the intervals from \(0\) to \(10\), \(10\) to \(20\), \(20\) to \(30\), \(30\) to \(40\), and \(40\) to \(50\) minutes, respectively.
2. The number in the \(10\)- to \(20\)-minute interval is \(0.35 \cdot 200 = 70\) students.
3. The interval midpoints are \(5, 15, 25, 35,\) and \(45\) minutes. The estimated mean is \((5 \cdot 0.20) + (15 \cdot 0.35) + (25 \cdot 0.25) + (35 \cdot 0.15) + (45 \cdot 0.05) = 20\) minutes.
Answer
a) \(0\)–\(10\) minutes: \(20\%\); \(10\)–\(20\) minutes: \(35\%\); \(20\)–\(30\) minutes: \(25\%\); \(30\)–\(40\) minutes: \(15\%\); \(40\)–\(50\) minutes: \(5\%\)
b) \(70\) students
c) Approximately \(20\) minutes