SAT Math : Factors / Multiples

Study concepts, example questions & explanations for SAT Math

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Example Questions

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Example Question #12 : How To Factor A Number

If    180 = 2^{a}3^{b}5^{c}7^{d}, where a,b,c,d are all positive integers, what is a+b+c+d?

Possible Answers:

3

6

4

5

7

Correct answer:

5

Explanation:

We will essentially have to represent 180 as a product of prime factors, because 2, 3, 5, and 7 are all prime numbers. The easiest way to do this will be to find the prime factorization of 180.

180 = 18(10)= (9)(2)(10) = (3)(3)(2)(10)=(3)(3)(2)(2)(5) = 2^{2}3^{2}5^{1}. Because 7 is not a factor of 180, we can mutiply the prime factorization of 180 by 7^{0} (which equals 1) in order to get 7 into our prime factorization.

180= 2^23^25^17^0= 2^a3^b5^c7^d

In order for 2^23^25^17^0 to equal 2^a3^b5^c7^d, the exponents of each base must match. This means that a = 2, b = 2, c = 1, and d = 0. The sum of a, b, c, and d is 5.

The answer is 5.

Example Question #13 : How To Factor A Number

What is the product of the distinct prime factors of 24?

Possible Answers:

\dpi{100} \small 5

\dpi{100} \small 6

\dpi{100} \small 8

\dpi{100} \small 9

\dpi{100} \small 24

Correct answer:

\dpi{100} \small 6

Explanation:

The prime factorization of 24 is (2)(2)(2)(3).  The distinct primes are 2 and 3, the product of which is 6.

Example Question #61 : Factors / Multiples

How many prime factors does \dpi{100} \small 2^{3}-1 have?

Possible Answers:

\dpi{100} \small 5

\dpi{100} \small 0

\dpi{100} \small 3

\dpi{100} \small 2

\dpi{100} \small 1

Correct answer:

\dpi{100} \small 1

Explanation:

\dpi{100} \small 2^{3}-1=8-1=7

Since 7 is prime, its only prime factor is itself.

Example Question #15 : How To Factor A Number

What is the smallest positive multiple of 12?

Possible Answers:

\dpi{100} \small 24

\dpi{100} \small 2

\dpi{100} \small 0

\dpi{100} \small 12

\dpi{100} \small 6

Correct answer:

\dpi{100} \small 12

Explanation:

Multiples of 12 are found by multiplying 12 by a whole number.  Some examples include:

\dpi{100} \small 12(-2)=-24

\dpi{100} \small 12(0)=0

\dpi{100} \small 12(1)=12

Clearly, the smallest positive value obtainable is 12.  Do not confuse the term multiple with the term factor!

Example Question #11 : How To Factor A Number

How many prime factors of 210 are greater than 2?

Possible Answers:

four

three

five

two

one

Correct answer:

three

Explanation:

Begin by identifying the prime factors of 210. This can be done easily using a factoring tree (see image).

Vt_p2

 

 The prime factors of 210 are 2, 3, 5 and 7. Of these factors, three of them are greater than 2. 

Example Question #11 : How To Factor A Number

How many integers between 50 and 100 are divisible by 9?

Possible Answers:

5

8

7

6

9

Correct answer:

6

Explanation:

The smallest multiple of 9 within the given range is \inline \dpi{200} \tiny 54 = 9 \times 6.

The largest multiple of 9 within the given range is \dpi{100} {99=9 \times 11}.

Counting the numbers from 6 to 11, inclusive, yields 6.

Example Question #61 : Factors / Multiples

  is the set of all positive multiples of , and  is the set of all squares of integers. Which of the following numbers belongs to both sets?

Possible Answers:

Correct answer:

Explanation:

 is the only choice that is both a multiple of  and a perfect square. 

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