PSAT Math : PSAT Mathematics

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #61 : Factors / Multiples

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:

4

5

3

7

6

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 #11 : How To Factor A Number

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

Possible Answers:

\dpi{100} \small 8

\dpi{100} \small 24

\dpi{100} \small 9

\dpi{100} \small 5

\dpi{100} \small 6

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 #12 : How To Factor A Number

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

Possible Answers:

\dpi{100} \small 2

\dpi{100} \small 0

\dpi{100} \small 1

\dpi{100} \small 5

\dpi{100} \small 3

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 #301 : Arithmetic

What is the smallest positive multiple of 12?

Possible Answers:

\dpi{100} \small 12

\dpi{100} \small 0

\dpi{100} \small 2

\dpi{100} \small 24

\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 #31 : Factors / Multiples

How many prime factors of 210 are greater than 2?

Possible Answers:

one

three

two

four

five

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 #32 : Factors / Multiples

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

Possible Answers:

8

7

6

9

5

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 #31 : Factors / Multiples

Possible Answers:

Correct answer:

Explanation:

Factor each number into prime roots:  

Example Question #1 : Basic Operations

Kacey works 5 hours per day on Monday, Tuesday, and Wednesday, as well as 9 hours on Thursday and Friday. She does not work on Saturday or Sunday. Her total earnings per week is $363. How much does she earn per hour in dollars?

Possible Answers:

8

9

12

11

Correct answer:

11

Explanation:

Kacey works 5 hours a day for 3 days and 9 hours a day for 2 days. (5)(3) = 15 and (2)(9) = 18. 15 + 18 = 33 hours worked a week. $363/33 hours = $11/hr.

Example Question #1861 : Psat Mathematics

When k is divided by 2, the remainder is 1. If k is divided by 3, the remainder is 0. And if k is divded by 5, the remainder is 3. Which of the following is a possible value for k?

Possible Answers:
30
57
63
23
27
Correct answer: 63
Explanation:

Since the remainder when k is divided by 2 is 1, this means that k is not an even number. Therefore, we can immediately eliminate 30 from our possible answer choices.

Because the remainder when k is divded by 3 is 0, we know that k must be a multiple of 3. This means we can eliminate 23 from our answer choices.

The only choices left are 63, 27, and 57. When 27 and 57 are divded by five, the remainder is two. Thus, only 63 works, because when 63 is divded by five, the remainder is three.

The answer is 63.

Example Question #1 : How To Divide Integers

The result of a number divided by 2 is the same as the result of that number divided by 10. What is that number?

Possible Answers:

1

0

2

10

Correct answer:

0

Explanation:

0 is the only choice that yields the same answer (0) when divided by 2 and 10. You can check this easily by plugging a few of the answer choices into a fraction:

1/2 ≠ 1/10

2/2 ≠ 2/10 etc.

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