Aimathic
Login | English | Deutsch

Grade 6 math worksheets

Build your own math worksheets from 35,000+ problems for grades 3 to 12, from fractions to AP Calculus. Every problem comes with step-by-step solutions.

Prime factorization and exponent notation

Learning goals

  • Writes composite numbers as products of prime factors.
  • Uses exponent notation for repeated prime factors.
  • Explains why all factors in a prime factorization must be prime.
  • Checks the factorization by multiplication.

Click problems to add them to your worksheet.

Prime factorization and exponent notation 1
Which is the correct prime factorization of \(720\)? a) \(8\times9\times10\) b) \(2\times5\times7\times11\) c) \(2^3\times3^2\times5\) d) \(2^4\times3^2\times5\)

Hints

- In a prime factorization, every factor must be prime. - Check whether every number in each choice is prime. - You can also evaluate each choice and compare it with \(720\).

Solution

1. Decompose \(720\) as \(72\times10\). 2. Factor each part into primes: \(72=8\times9=2\times2\times2\times3\times3\), and \(10=2\times5\). 3. Combine repeated prime factors: \(2\times2\times2\times2\times3\times3\times5=2^4\times3^2\times5\).

Answer

d) \(2^4\times3^2\times5\)
Prime factorization and exponent notation 2
Write \(18\) as a product of prime factors.

Hints

- Start with any factor pair for \(18\). - Continue factoring any factor that is composite. - Stop when every factor is prime.

Solution

1. Split \(18\) into \(2\times9\). 2. Factor \(9\) as \(3\times3\). 3. All factors are prime, so \(18=2\times3\times3=2\times3^2\).

Answer

\(18=2\times3^2\)
Prime factorization and exponent notation 3
Finish the prime factorization of \(18=2\times9\). Write the answer as a product of primes.

Hints

- Check whether each factor shown is prime. - If a factor can be split into smaller whole-number factors, keep going. - Multiply the final prime factors to check the original number.

Solution

1. The factor \(9\) is not prime because \(9=3\times3\). 2. Substitute to obtain \(18=2\times3\times3\).

Answer

\(2\times3\times3\)
Prime factorization and exponent notation 4
Write \(3\times3\times3\times5\times5\) using exponents. Explain what each exponent counts.

Hints

- Group identical factors. - Count how often each different factor appears. - Keep the two different prime bases separate.

Solution

1. The factor \(3\) appears three times, so write \(3^3\). 2. The factor \(5\) appears twice, so write \(5^2\). 3. The product is \(3^3\times5^2\).

Answer

\(3^3\times5^2\); the exponents count three copies of \(3\) and two copies of \(5\).
Prime factorization and exponent notation 5
Two students write products for \(30\). Mia writes \(2\times3\times5\); Ben writes \(3\times10\). Both products equal \(30\). Which one is a prime factorization, and why?

Hints

- Both products multiply to \(30\), so the final value alone does not settle the question. - Look at each factor, one at a time, rather than the product as a whole. - Try finding a factor pair for any factor you are unsure about.

Solution

1. Both products equal \(30\). 2. Mia's factors \(2\), \(3\), and \(5\) are all prime. 3. Ben's product contains the composite factor \(10\), so only Mia's product is a prime factorization.

Answer

Mia's \(2\times3\times5\) is the prime factorization. Ben's product contains the composite factor \(10\).
Prime factorization and exponent notation 6
1) Find the prime factorization of each number and write it as a power of one prime number: \(81\), \(125\), and \(64\). 2) Find the prime factorizations of \(200\) and \(450\). Use exponents for repeated prime factors.

Hints

- Factor each number until every factor is prime. - How can repeated equal prime factors be written using an exponent? - Begin with the smallest prime numbers.

Solution

1. Factor each prime power: \(81=3\times3\times3\times3=3^4\), \(125=5\times5\times5=5^3\), and \(64=2\times2\times2\times2\times2\times2=2^6\). 2. Factor the remaining numbers: \(200=2\times2\times2\times5\times5=2^3\times5^2\), and \(450=2\times3\times3\times5\times5=2\times3^2\times5^2\).

Answer

1) \(81=3^4\); \(125=5^3\); \(64=2^6\) 2) \(200=2^3\times5^2\); \(450=2\times3^2\times5^2\)
Prime factorization and exponent notation 7
Use repeated factors to evaluate \(2^3\times2^2\). Then write the product as a single power of \(2\).

Hints

- Rewrite each power as repeated multiplication. - Count the total number of factors equal to \(2\). - Use that count as the exponent in the single power.

Solution

1. Expand the powers: \(2^3\times2^2=(2\times2\times2)(2\times2)\). 2. There are five factors of \(2\), so the product is \(2^5\). 3. Evaluate \(2^5=32\).

Answer

\(2^3\times2^2=2^5=32\)
Prime factorization and exponent notation 8
Complete the prime factorization \(200=2^a\times5^b\). a) Find \(a\) and \(b\). b) Write the expanded product of prime factors.

Hints

- Break the number into powers of the two listed primes. - Use each exponent to count repeated factors. - Multiply the expanded factors to check the result.

Solution

1. Factor \(200=8\times25\). 2. Write \(8=2^3\) and \(25=5^2\). 3. Therefore, \(a=3\), \(b=2\), and the expanded product is \(2\times2\times2\times5\times5\).

Answer

a) \(a=3\), \(b=2\) b) \(2\times2\times2\times5\times5\)
Prime factorization and exponent notation 9
A number has prime factorization \(2\times2\times2\times5\). a) Rewrite the factorization using an exponent. b) What is the number?

Hints

- Count how many times each prime factor repeats. - Use that count as an exponent. - Evaluate the exponent before multiplying by the remaining prime factor.

Solution

1. The prime factor \(2\) appears three times, so \(2\times2\times2=2^3\). 2. The factorization is \(2^3\times5\). 3. Evaluate: \(2^3\times5=8\times5=40\).

Answer

a) \(2^3\times5\) b) \(40\)
Prime factorization and exponent notation 10
Which whole number has the prime factorization \(2^3\times3^2\)? Show how to build it from the prime powers.

Hints

- Work out each power as repeated multiplication. - Multiply the two prime-power values. - Check that the result contains exactly the requested prime copies.

Solution

1. Evaluate the powers: \(2^3=8\) and \(3^2=9\). 2. Multiply \(8\times9=72\).

Answer

\(2^3=8\) and \(3^2=9\), so \(2^3\times3^2=8\times9=72\).
Prime factorization and exponent notation 11
A student writes \(90=2\times3\times5^2\) as its prime factorization. Check the product. Correct the factorization and explain which prime appears too many times and which appears too few times.

Hints

- Find the value of the student's product first. - Write the actual number as a product of primes. - Compare the copies of each prime in the two products.

Solution

1. The student's product is \(2\times3\times25=150\), not \(90\). 2. The correct factorization is \(90=2\times3\times3\times5=2\times3^2\times5\). 3. The student's product has one too many factors of \(5\) and one too few factors of \(3\).

Answer

The claimed product is \(150\), not \(90\). The student used two factors of \(5\) instead of one and only one factor of \(3\) instead of two. Correct: \(90=2\times3^2\times5\).
Prime factorization and exponent notation 12
Find the prime factorization of each number and write it using exponents, such as \(2^2\times3\): \(60,126,\) and \(270\). Which prime factors are common to all three numbers?

Hints

- Recall the definition of a prime number. - Decompose each number until every factor is prime. - Count how many times each prime factor appears. - Compare the three lists of prime factors.

Solution

1. Factor \(60\): \(60=2\times30=2\times2\times15=2^2\times3\times5\). 2. Factor \(126\): \(126=2\times63=2\times3\times21=2\times3^2\times7\). 3. Factor \(270\): \(270=2\times135=2\times3\times45=2\times3^2\times15=2\times3^3\times5\). 4. The prime factors \(2\) and \(3\) appear in all three factorizations.

Answer

\(60=2^2\times3\times5\) \(126=2\times3^2\times7\) \(270=2\times3^3\times5\) The common prime factors are \(2\) and \(3\).
Prime factorization and exponent notation 13
A number \(n\) has prime factorization \(2^2\times3\times7\). a) What is the value of \(n\)? b) What is the prime factorization of the number that is exactly five times \(n\)? c) Explain without calculating why a number greater than \(5\) that ends in \(5\) can never be prime.

Hints

- What happens to a prime factorization when the number is multiplied by another prime number? - Which ones digits indicate divisibility by \(5\)? - How many positive factors does a prime number have?

Solution

1. Evaluate the factorization: \(n=2^2\times3\times7=4\times3\times7=84\). 2. Multiplying \(n\) by \(5\) adds one factor of \(5\). The new prime factorization is \(2^2\times3\times5\times7\). 3. Every number ending in \(5\) is divisible by \(5\). If the number is greater than \(5\), then it has at least the positive factors \(1\), \(5\), and itself, so it is not prime.

Answer

a) \(n=84\) b) \(2^2\times3\times5\times7\) c) A number greater than \(5\) that ends in \(5\) is divisible by \(5\), so it has more than two positive factors and is not prime.
Prime factorization and exponent notation 14
Use prime factorization to generate the required factors. a) The sum of two positive integers is \(21\), and their product is \(108\). Prime-factorize \(108\), use that factorization to generate its positive factor pairs, and determine the two integers. b) The product of three different positive integers is \(180\). Prime-factorize \(180\) using exponent notation, then use the factorization to give one set of three different factors whose product is \(180\).

Hints

- Start from the prime factorization so your factor-pair list is complete. - For part a, compare the sum of each generated factor pair with \(21\). - For part b, group the prime factors into three different positive factors. - Check that every reported factor comes from the prime factorization.

Solution

1. For a), \(108=2^2\times3^3\). Its positive factor pairs are \((1,108),(2,54),(3,36),(4,27),(6,18),(9,12)\). 2. The factor pair whose sum is \(21\) is \(9\) and \(12\). 3. For b), \(180=2^2\times3^2\times5\). One grouping of the prime factors gives \(2\times9\times10=180\), and the factors \(2,9,10\) are different.

Answer

a) \(9\) and \(12\) b) For example, \(2\), \(9\), and \(10\)
Prime factorization and exponent notation 15
Prime-factorize each number and write repeated prime factors with exponent notation. a) \(3600\) b) \(294\) c) Use the two prime factorizations to decide whether \(42\) is a factor of each number. Justify your answer from the prime factors rather than by dividing.

Hints

- Break each composite number into smaller factors until every factor is prime. - Collect repeated prime factors with exponents. - Prime-factorize \(42\) before comparing it with the other factorizations. - A number is divisible by \(42\) only if its prime factorization contains all prime factors required by \(42\).

Solution

1. \(3600=36\times100=(2^2\times3^2)(2^2\times5^2)=2^4\times3^2\times5^2\). 2. \(294=2\times147=2\times3\times49=2\times3\times7^2\). 3. Since \(42=2\times3\times7\), a number must contain at least one factor each of \(2\), \(3\), and \(7\) in its prime factorization to be divisible by \(42\). 4. The factorization of \(3600\) has no factor \(7\), so \(42\) is not a factor of \(3600\). 5. The factorization of \(294\) contains \(2\), \(3\), and \(7^2\), so \(42\) is a factor of \(294\).

Answer

a) \(3600=2^4\times3^2\times5^2\) b) \(294=2\times3\times7^2\) c) \(42\) is not a factor of \(3600\), but it is a factor of \(294\).
Prime factorization and exponent notation 16
Consider the number \(130\). a) Find the prime factorization of \(130\). b) Use the prime factorization to list all positive factors of \(130\). c) How many positive factors does \(130\) have?

Hints

- Continue factoring until every factor is prime. - Each positive factor can be made by multiplying some of the prime factors. - Remember to include \(1\) and the number itself. - Organize the products systematically so that none are missed.

Solution

1. Factor the number: \(130=2\times65=2\times5\times13\). 2. Form every possible product using each prime factor either once or not at all: \(1,2,5,13,2\times5,2\times13,5\times13,\) and \(2\times5\times13\). 3. In numerical order, the positive factors are \(1,2,5,10,13,26,65,\) and \(130\). Therefore, \(130\) has \(8\) positive factors.

Answer

a) \(130=2\times5\times13\) b) \(1,2,5,10,13,26,65,130\) c) \(8\) positive factors
Prime factorization and exponent notation 17
Compare the numbers of positive factors of two products of primes. a) How many positive factors does \(6=2\times3\) have? b) How many positive factors does \(9=3\times3\) have? c) Explain why the numbers of factors are different even though both numbers are products of two prime factors.

Hints

- List all positive factors of each number. - Compare the prime factors in the two factorizations. - How is multiplying two equal primes different from multiplying two distinct primes?

Solution

1. The positive factors of \(6\) are \(1,2,3,\) and \(6\), so \(6\) has \(4\) positive factors. 2. The positive factors of \(9\) are \(1,3,\) and \(9\), so \(9\) has \(3\) positive factors. 3. The prime factors of \(6\) are distinct, so each creates a different factor. In \(9=3^2\), the two prime factors are the same, so they do not create two different one-prime factors.

Answer

a) \(4\) positive factors: \(1,2,3,6\) b) \(3\) positive factors: \(1,3,9\) c) The number \(6\) has two distinct prime factors, while \(9\) repeats the same prime factor. Repetition produces fewer distinct products.
Prime factorization and exponent notation 18
a) Find the prime factorization of \(72\). b) Use the prime factorization to find all positive factors of \(72\) that are between \(10\) and \(30\).

Hints

- Continue factoring until every factor is prime. - Positive factors are made by multiplying allowable numbers of the prime factors. - Try different combinations of the prime factors. - Check systematically which products are between \(10\) and \(30\).

Solution

1. Factor repeatedly: \(72=2\times36=2\times2\times18=2\times2\times2\times9=2^3\times3^2\). 2. Form factor products in the requested interval: \(2^2\times3=12\), \(2\times3^2=18\), and \(2^3\times3=24\). 3. Other nearby products, such as \(2^3=8\), \(3^2=9\), and \(2^2\times3^2=36\), are outside the interval. Therefore, the requested factors are \(12,18,\) and \(24\).

Answer

a) \(72=2^3\times3^2\) b) \(12,18,24\)
Prime factorization and exponent notation 19
The prime factorization of \(150\) is \(2\times3\times5^2\). Decide whether each statement is true or false. Briefly justify each answer using the prime factorization. a) \(15\) is a factor of \(150\). b) \(20\) is a factor of \(150\). c) \(25\) is a factor of \(150\).

Hints

- What must be true about the prime factors of a factor of a number? - Find the prime factorizations of \(15\), \(20\), and \(25\). - Check whether \(150\) contains every required prime factor enough times.

Solution

1. Since \(15=3\times5\), and \(150\) contains both required prime factors, \(15\) is a factor of \(150\). 2. Since \(20=2^2\times5\), it requires two factors of \(2\). The factorization of \(150\) contains only one factor of \(2\), so \(20\) is not a factor. 3. Since \(25=5^2\), and \(150\) contains two factors of \(5\), \(25\) is a factor.

Answer

a) True, because \(15=3\times5\), and both prime factors occur in \(150\). b) False, because \(20=2^2\times5\), but \(150\) contains only one factor of \(2\). c) True, because \(25=5^2\), and \(150\) contains two factors of \(5\).
Prime factorization and exponent notation 20
A number \(n\) has prime factorization \(2^2\times3\times11\). a) Find the value of \(n\). b) Give one factor of \(n\) that is between \(10\) and \(20\). c) Explain using the prime factorization why \(9\) is not a factor of \(n\).

Hints

- Multiply the factors in stages to find \(n\). - Which individual prime factors or products of factors are between \(10\) and \(20\)? - Find the prime factorization of \(9\). - Compare how many factors of \(3\) are required with how many occur in \(n\).

Solution

1. Evaluate the factorization: \(n=2^2\times3\times11=4\times3\times11=132\). 2. The prime factor \(11\) is between \(10\) and \(20\). Another possible factor is \(2^2\times3=12\). 3. Since \(9=3^2\), a number divisible by \(9\) must contain at least two factors of \(3\). The factorization of \(n\) contains only one factor of \(3\), so \(9\) is not a factor of \(n\).

Answer

a) \(n=132\) b) Possible answers include \(11\) and \(12\). c) Since \(9=3^2\) but \(n\) contains only one factor of \(3\), \(9\) is not a factor of \(n\).
Prime factorization and exponent notation 21
Find the prime factorization of \(756\). Write the repeated prime factors using exponents, and state how many times the prime \(3\) occurs.

Hints

- Break \(756\) into factors that are easier to factor again. - Continue until every factor is prime. - Use an exponent to count repeated copies of the same prime.

Solution

1. Factor \(756=4\times189\). 2. Write \(4=2^2\) and \(189=27\times7=3^3\times7\). 3. Therefore, \(756=2^2\times3^3\times7\), so the prime \(3\) occurs three times. 4. Check: \(2^2\times3^3\times7=4\times27\times7=756\).

Answer

\(756=2^2\times3^3\times7\); the prime \(3\) occurs three times.
Prime factorization and exponent notation 22
A number has prime factorization \(2^4\times3\times5^2\). a) Find the number. b) How many prime factors are shown if repeated factors are counted separately? c) How many distinct prime factors does the number have?

Hints

- Evaluate each exponent before multiplying the factors. - Use the exponents to count repeated prime factors. - Count prime bases, not exponents, for the distinct-factor question.

Solution

1. Evaluate the prime powers: \(2^4=16\) and \(5^2=25\). 2. Multiply: \(16\times3\times25=1200\). 3. Counting repeats gives \(4+1+2=7\) prime factors, and the distinct primes are \(2,3,5\), so there are \(3\) distinct prime factors.

Answer

a) \(1200\) b) \(7\) c) \(3\)
Prime factorization and exponent notation 23
A number is divisible by \(9\), and dividing it by \(9\) gives \(77\). Write the number's prime factorization and find the number.

Hints

- Factor both the divisor and the quotient. - Combine all prime factors before evaluating the number. - Check by dividing the final number by the given divisor.

Solution

1. Write \(9=3^2\) and \(77=7\times11\). 2. Combine the prime factors to get \(3^2\times7\times11\). 3. The number is \(9\times77=693\).

Answer

Prime factorization: \(3^2\times7\times11\); number: \(693\)
Prime factorization and exponent notation 24
Without using a calculator, compare \(A=2^3\times3^2\) and \(B=2^2\times3\times5\). a) Find each value. b) Write \(<\), \(>\), or \(=\) to complete \(A\ \square\ B\). c) Which expression contains more prime factors when repeats are counted?

Hints

- Evaluate the powers before multiplying. - Compare the final whole-number values. - Add exponents to count repeated prime factors.

Solution

1. Evaluate \(A=8\times9=72\). 2. Evaluate \(B=4\times3\times5=60\). 3. Therefore, \(A>B\). 4. Expression \(A\) has \(3+2=5\) prime factors, while \(B\) has \(2+1+1=4\), so \(A\) has more.

Answer

a) \(A=72\), \(B=60\) b) \(>\) c) \(A\)
Prime factorization and exponent notation 25
Let \(N=2^3\times3\times7\). Decide whether \(N\) is divisible by each number. Justify using prime factors. a) \(24\) b) \(28\) c) \(18\)

Hints

- Factor each possible divisor into primes. - Compare how many copies of each prime are required. - A missing repeated prime factor prevents divisibility.

Solution

1. The factorization is \(N=2^3\times3\times7\). 2. Since \(24=2^3\times3\), all its prime factors occur in \(N\), so \(N\) is divisible by \(24\). 3. Since \(28=2^2\times7\), all its prime factors occur in \(N\), so \(N\) is divisible by \(28\). 4. Since \(18=2\times3^2\) requires two factors of \(3\) but \(N\) has one, \(N\) is not divisible by \(18\).

Answer

a) Yes. b) Yes. c) No.
Prime factorization and exponent notation 26
A composite number is made from exactly three factors of \(2\), two factors of \(3\), and one factor of \(5\), with no other prime factors. a) Write its prime factorization using exponents. b) Find the number. c) Explain why \(180\) does not meet the description.

Hints

- Translate each repeated-factor count into an exponent. - Evaluate the prime powers before multiplying. - Factor the comparison number to identify the mismatch.

Solution

1. The prime factorization is \(2^3\times3^2\times5\). 2. Its value is \(8\times9\times5=360\). 3. Since \(180=2^2\times3^2\times5\), it has only two factors of \(2\), not three.

Answer

a) \(2^3\times3^2\times5\) b) \(360\) c) \(180\) has only \(2^2\), so it is missing one factor of \(2\).
Prime factorization and exponent notation 27
Factor \(1323\) completely. Write the prime factorization using exponents, then verify it by multiplication.

Hints

- Use a divisibility test to choose a small prime factor. - Continue dividing until the quotient is no longer divisible by that prime. - Rewrite repeated primes with exponents and multiply to check.

Solution

1. The digit sum is \(9\), so divide repeatedly by \(3\): \(1323=3\times441=3\times3\times147=3^3\times49\). 2. Write \(49=7^2\). 3. Therefore, \(1323=3^3\times7^2\). 4. Verification: \(27\times49=1323\).

Answer

\(1323=3^3\times7^2\)
Prime factorization and exponent notation 28
The prime factorization of \(132\) is \(2^2\times3\times p\), where \(p\) is prime. a) Find \(p\). b) Explain how you know \(p\) is prime.

Hints

- Multiply the known prime factors first. - Use the original number to find the missing factor. - Check the factor against the definition of a prime number.

Solution

1. The known factors multiply to \(2^2\times3=12\). 2. The missing factor is \(132\div12=11\). 3. The number \(11\) has only factors \(1\) and \(11\), so it is prime.

Answer

a) \(p=11\) b) \(11\) has exactly two positive factors, \(1\) and \(11\).
Prime factorization and exponent notation 29
A number \(M\) has prime factorization \(2^5\times3^2\times5\). Divide \(M\) by \(2^2\times3\). a) Write the quotient in prime-factor form. b) Find the quotient's value.

Hints

- Expand the exponents mentally as repeated prime factors. - Cancel only the copies contained in the divisor. - Evaluate the remaining prime powers last.

Solution

1. Remove two factors of \(2\) from the five and one factor of \(3\) from the two. 2. The quotient is \(2^3\times3\times5\). 3. Its value is \(8\times3\times5=120\).

Answer

a) \(2^3\times3\times5\) b) \(120\)
Prime factorization and exponent notation 30
A number \(K\) has prime factorization \(2^3\times3^2\). The number is multiplied by \(15\). a) Write \(15\) as a product of primes. b) Write the prime factorization of \(15K\). c) Which exponents or prime bases change from \(K\) to \(15K\)?

Hints

- Factor the multiplier before combining it with the given factorization. - Group equal prime factors together. - Compare the original and final prime bases and exponents.

Solution

1. The prime factorization of \(15\) is \(3\times5\). 2. Combine factors: \(15K=2^3\times3^2\times3\times5=2^3\times3^3\times5\). 3. The exponent on \(3\) increases from \(2\) to \(3\), and the new prime base \(5\) appears.

Answer

a) \(15=3\times5\) b) \(15K=2^3\times3^3\times5\) c) The exponent on \(3\) increases by one, and a factor of \(5\) is added.
Prime factorization and exponent notation 31
Consider numbers of the form \(2^a\times3\), where \(a\) can be \(1\), \(2\), or \(3\). a) Find the three numbers. b) Describe how each number changes when \(a\) increases by \(1\). c) Which prime factor is repeated more often as \(a\) increases?

Hints

- Evaluate each allowed exponent separately. - Compare consecutive values rather than all three at once. - Interpret what increasing an exponent does to repeated factors.

Solution

1. For \(a=1\), the number is \(2\times3=6\). 2. For \(a=2\), the number is \(4\times3=12\); for \(a=3\), it is \(8\times3=24\). 3. Each increase of one in \(a\) adds another factor of \(2\), so the value doubles and the prime \(2\) repeats more often.

Answer

a) \(6, 12, 24\) b) Each number doubles. c) The prime factor \(2\)
Prime factorization and exponent notation 32
Which expression is the prime factorization of \(864\)? Explain why the other choices fail. A: \(2^5\times3^3\) B: \(2^4\times3^3\) C: \(2^5\times27\)

Hints

- Check both the numerical value and whether every base is prime. - Evaluate each expression before deciding. - A product can equal \(864\) and still fail to be a prime factorization.

Solution

1. Choice A equals \(32\times27=864\), and both bases \(2\) and \(3\) are prime. 2. Choice B equals \(16\times27=432\), so it does not have the correct value. 3. Choice C equals \(32\times27=864\), but \(27\) is composite, so the expression is not fully factored into primes.

Answer

A: \(2^5\times3^3\)
Prime factorization and exponent notation 33
Number \(A\) has prime factorization \(2^2\times3\times13\). Number \(B\) is formed by replacing the factor \(13\) with \(5\), leaving all other prime factors unchanged. a) Find \(A\) and \(B\). b) Write the prime factorization of \(B\). c) Which number is greater, and why can you decide before multiplying everything?

Hints

- Identify the factors shared by both numbers. - Evaluate each prime-power product carefully. - Compare the one factor that differs.

Solution

1. Evaluate \(A=4\times3\times13=156\). 2. The factorization of \(B\) is \(2^2\times3\times5\), so \(B=4\times3\times5=60\). 3. Number \(A\) is greater because the common factor \(2^2\times3\) is multiplied by \(13\) instead of \(5\).

Answer

a) \(A=156\), \(B=60\) b) \(2^2\times3\times5\) c) \(A\) is greater because \(13>5\) while the remaining factors are identical.
Prime factorization and exponent notation 34
A fraction in simplest form can be rewritten with a power of \(10\) as its denominator only when the denominator has no prime factors other than \(2\) and \(5\). a) Explain why \(\frac{1}{8}\) can be rewritten with denominator \(1000\), but not with denominator \(100\). b) Find the smallest power of \(10\) that can be used as a denominator for an equivalent fraction to \(\frac{7}{40}\). c) Give one denominator from \(10\) through \(15\) for which a fraction in simplest form cannot be rewritten with a power of \(10\) as its denominator. Explain.

Hints

- Write each denominator as a product of prime factors. - A power of \(10\) has equal numbers of factors of \(2\) and \(5\). - Look for a denominator containing a prime factor other than \(2\) or \(5\).

Solution

1. For a), \(8=2^3\). Since \(100=2^2\times5^2\), \(8\) is not a factor of \(100\). Since \(1000=2^3\times5^3\), \(8\) is a factor of \(1000\). 2. For b), \(40=2^3\times5\). The smallest power of \(10\) containing at least three factors of \(2\) and one factor of \(5\) is \(10^3=1000\). 3. For c), one answer is \(12\), because \(12=2^2\times3\) contains a factor of \(3\), and powers of \(10\) contain only factors of \(2\) and \(5\).

Answer

a) \(8\) is a factor of \(1000\), but not of \(100\). b) \(1000\) c) For example, \(12\), because it contains the prime factor \(3\).
Prime factorization and exponent notation 35
Use the prime factorization \(1000=2^3\times5^3\) throughout. a) Generate all positive divisors \(n\le100\) of \(1000\) by choosing allowable exponents of \(2\) and \(5\). List the divisors. b) A fraction with denominator \(m\) was multiplied by \(\frac{8}{8}\) to produce denominator \(1000\). Use prime factors to find \(m\). Then give three proper fractions with denominator \(m\) that are already in simplest form, explaining the numerator restriction from the prime factorization of \(m\).

Hints

- A divisor of \(2^3\times5^3\) can use only the primes \(2\) and \(5\), with exponents no larger than \(3\). - For part b, express \(8\) as a power of \(2\) and remove those prime factors from \(1000\). - A common factor with \(125\) must involve which prime?

Solution

1. Every divisor of \(1000=2^3\times5^3\) has the form \(2^a5^b\) with \(0\le a,b\le3\). 2. Keeping only values at most \(100\) gives \(1,2,4,5,8,10,20,25,40,50,100\). 3. Since \(8=2^3\), dividing the prime factorization of \(1000\) by \(8\) leaves \(5^3=125\). Thus \(m=125\). 4. A fraction with denominator \(125=5^3\) is in simplest form when its numerator is not divisible by \(5\). Examples are \(\frac{1}{125},\frac{2}{125},\frac{3}{125}\).

Answer

a) Every divisor has the form \(2^a5^b\) with \(0\le a,b\le3\). Those at most \(100\) are \(1,2,4,5,8,10,20,25,40,50,100\). b) \(m=125=5^3\); for example, \(\frac{1}{125},\frac{2}{125},\frac{3}{125}\). The numerator must not be divisible by \(5\).
Prime factorization and exponent notation 36
Use prime factorization, not trial substitution, to solve the puzzle. The symbol \(\triangle\) is a positive natural number less than \(12\). Find every value of \(\triangle\) for which \( 3\frac{\triangle}{12}+\frac56 \) is a natural number. Your work must include the prime factorization of \(12\) and a divisibility argument using its prime factors.

Hints

- Combine the mixed number and fraction into one fraction with denominator \(12\). - Prime-factorize \(12\) using exponent notation. - A numerator divisible by \(12=2^2\times3\) must be divisible by both \(4\) and \(3\). - Use the allowed range of \(\triangle\) to narrow the possible numerator values.

Solution

1. Write the expression with denominator \(12\): \( 3\frac{\triangle}{12}+\frac56=\frac{36+\triangle+10}{12}=\frac{46+\triangle}{12}. \) 2. Prime-factorize the denominator: \(12=2^2\times3\). Therefore, \(46+\triangle\) must be divisible by both \(4\) and \(3\). 3. Since \(1\le\triangle\le11\), the numerator \(46+\triangle\) lies from \(47\) through \(57\). 4. In this interval, the only number divisible by both \(4\) and \(3\) is \(48\). 5. Thus \(46+\triangle=48\), so \(\triangle=2\). The value of the expression is \(48/12=4\).

Answer

\(\triangle=2\), and the expression equals \(4\).
Prime factorization and exponent notation 37
A rectangular floor is covered with \(360\) square tiles arranged in whole rows and columns. The number of rows is a multiple of \(8\), and the number of columns is a multiple of \(5\). Find every possible ordered pair (rows, columns). Use the prime factorization of \(360\) to show that your list is complete.

Hints

- Write the total number of tiles as a product of prime factors. - Think about the factors each dimension must contain to satisfy the divisibility conditions. - How can you account for every possible use of the remaining factors?

Solution

1. The prime factorization is \(360=2^3\times3^2\times5\). 2. The rows must use at least \(2^3\) and the columns must use at least \(5\). These required factors use \(8\times5=40\) of the product. 3. The remaining factor is \(3^2=9\). It can be split between rows and columns as \(1\times9\), \(3\times3\), or \(9\times1\). 4. This gives \((8,45)\), \((24,15)\), and \((72,5)\). Each pair has product \(360\), and there are no other ways to distribute the remaining factors.

Answer

\((8,45)\), \((24,15)\), and \((72,5)\). Since \(360=2^3\times3^2\times5\), the required row factor \(8\) and column factor \(5\) leave \(3^2\), which can be divided between the dimensions in exactly three ways.
Prime factorization and exponent notation 38
Two numbers are given by their prime factorizations: \(A=2^2\times3\times5\) and \(B=2\times3^2\times5\). a) Find the values of \(A\) and \(B\). b) Find the prime factorization of \(A\times B\). c) What is the least prime number that is not a factor of either \(A\) or \(B\)? d) Is \(A+B\) divisible by \(5\)? Justify your answer using the prime factorizations without first finding the sum.

Hints

- How can you combine two products of prime factors into one product? - Identify which primes appear in either factorization, then consider the least prime absent from both. - If two numbers share a factor, what does that tell you about their sum?

Solution

1. Evaluate each factorization: \(A=4\times3\times5=60\) and \(B=2\times9\times5=90\). 2. Combine like prime factors in the product: \(A\times B=(2^2\times3\times5)(2\times3^2\times5)=2^{2+1}\times3^{1+2}\times5^{1+1}=2^3\times3^3\times5^2\). 3. The primes \(2\), \(3\), and \(5\) occur in at least one of the factorizations. The next prime, \(7\), occurs in neither. 4. Both \(A\) and \(B\) contain a factor of \(5\), so both are multiples of \(5\). The sum of two multiples of \(5\) is also divisible by \(5\).

Answer

a) \(A=60\), \(B=90\) b) \(2^3\times3^3\times5^2\) c) \(7\) d) Yes. Both numbers contain a factor of \(5\), so their sum is divisible by \(5\).
Prime factorization and exponent notation 39
Find a natural number \(x\) that satisfies all three conditions. 1. \(30<x<50\) 2. \(x\) is a multiple of \(3\). 3. \(x\) has exactly \(6\) positive factors. Use prime factorizations to justify your choice. Give the number and list all its factors.

Hints

- First list the multiples of \(3\) in the interval. - Write the prime factorization of each candidate. - Think about how many exponent choices each prime factor allows when building a positive factor.

Solution

1. The multiples of \(3\) between \(30\) and \(50\) are \(33,36,39,42,45,48\). 2. Their prime factorizations are \(33=3\times11\), \(36=2^2\times3^2\), \(39=3\times13\), \(42=2\times3\times7\), \(45=3^2\times5\), and \(48=2^4\times3\). 3. For a prime factorization, a factor can use each prime exponent from \(0\) through its exponent in the number. Thus \(33\) and \(39\) each have \(2\times2=4\) factors; \(36\) has \(3\times3=9\); \(42\) has \(2\times2\times2=8\); \(45\) has \(3\times2=6\); and \(48\) has \(5\times2=10\). 4. The factors of \(45\) are \(1,3,5,9,15,45\), so \(x=45\).

Answer

\(x=45\); its factors are \(1,3,5,9,15,45\).
Prime factorization and exponent notation 40
Solve the number riddle using prime factorization and the factor-count rule. Do not solve it by listing common multiples. My number is less than \(100\). It is divisible by both \(4\) and \(9\). It has exactly nine positive factors. What is my number?

Hints

- Translate divisibility by \(4\) and \(9\) into minimum prime exponents. - Use the exponent rule for counting positive factors. - Ask whether any extra prime factor or larger exponent could keep the factor count at exactly nine.

Solution

1. Divisibility by \(4=2^2\) and \(9=3^2\) means the number’s prime factorization must contain at least \(2^2\times3^2\). 2. A number with prime factorization \(p^a q^b\) has \((a+1)(b+1)\) positive factors. 3. The required exponents \(2\) and \(2\) already give \((2+1)(2+1)=9\) factors. 4. Increasing either exponent or adding another prime factor would make the factor count greater than \(9\). 5. Therefore, the number is exactly \(2^2\times3^2=36\), which is less than \(100\).

Answer

\(36\)
Prime factorization and exponent notation 41
Let \(N=2^4\times3^2\). a) Find \(N\). b) Regroup the prime factors to write \(N\) as the square of a whole number. c) Explain how the even exponents make the regrouping possible.

Hints

- Think of each exponent as a count of repeated prime factors. - Divide each repeated-factor count into two equal groups. - Multiply one group to find the number being squared.

Solution

1. Evaluate \(N=16\times9=144\). 2. Pair equal prime factors: \(2^4\times3^2=(2^2\times3)^2=12^2\). 3. Each even exponent splits into two equal groups of prime factors.

Answer

a) \(144\) b) \(N=12^2\) c) Even exponents allow every repeated prime factor to be paired equally between the two copies of \(12\).
Prime factorization and exponent notation 42
Suppose \(n\) is the product of four distinct prime numbers \(a\), \(b\), \(c\), and \(d\), so \(n=abcd\). a) Use the letters to list all positive factors of \(n\). b) Find the total number of positive factors of \(n\). c) Check your result by listing the positive factors of \(210=2\times3\times5\times7\).

Hints

- Organize the factors by how many of the four primes are used. - How many ways can you choose none, one, two, three, or all four letters? - A tree diagram or table can help you find every combination.

Solution

1. Group the factors by the number of prime factors used. Using none gives \(1\). Using one gives \(a,b,c,d\). Using two gives \(ab,ac,ad,bc,bd,cd\). Using three gives \(abc,abd,acd,bcd\). Using all four gives \(abcd\). 2. The number of factors is \(1+4+6+4+1=16\). 3. For \(210=2\times3\times5\times7\), the positive factors are \(1,2,3,5,6,7,10,14,15,21,30,35,42,70,105,\) and \(210\). This list has \(16\) factors, confirming the result.

Answer

a) \(1\); \(a,b,c,d\); \(ab,ac,ad,bc,bd,cd\); \(abc,abd,acd,bcd\); \(abcd\) b) \(16\) positive factors c) \(1,2,3,5,6,7,10,14,15,21,30,35,42,70,105,210\)

All problems may be used, copied and printed free of charge for school and tutoring, including paid tutoring. Commercial adaptations as well as publication or redistribution on the internet are not permitted.