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The "prime sum" of an integer n greater than 1 is

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by swerve » Fri Apr 20, 2018 8:13 am
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The "prime sum" of an integer n greater than 1 is the sum of all the prime factors of n, including repetitions. For example , the prime sum of 12 is 7, since 12 = 2 x 2 x 3 and 2 +2 + 3 = 7. For which of the following integers is the prime sum greater than 35?

A. 440
B. 512
C. 620
D. 700
E. 750

The OA is C.

Please, can anyone explain this PS question? I can't get the correct answer. Thanks.
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The "prime sum" of an integer n greater than 1 is

by Brent@GMATPrepNow » Fri Apr 20, 2018 12:17 pm
swerve wrote:The "prime sum" of an integer n greater than 1 is the sum of all the prime factors of n, including repetitions. For example , the prime sum of 12 is 7, since 12 = 2 x 2 x 3 and 2 +2 + 3 = 7. For which of the following integers is the prime sum greater than 35?

A. 440
B. 512
C. 620
D. 700
E. 750
This question requires us to find the prime factorization of the answer choices
A. 440 = (2)(2)(2)(5)(11).
PRIME SUM = 2 + 2 + 2 + 5 + 11 = 22

B. 512 = (2)(2)(2)(2)(2)(2)(2)(2)(2)
PRIME SUM = 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 + 2 = 18

C. 620 = (2)(2)(5)(31)
PRIME SUM = 2 + 2 + 5 + 31 = 40

STOP right there.
We've found the number that has a prime sum that's greater than 35.

Answer: C

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by Scott@TargetTestPrep » Wed Apr 25, 2018 3:47 pm
swerve wrote:The "prime sum" of an integer n greater than 1 is the sum of all the prime factors of n, including repetitions. For example , the prime sum of 12 is 7, since 12 = 2 x 2 x 3 and 2 +2 + 3 = 7. For which of the following integers is the prime sum greater than 35?

A. 440
B. 512
C. 620
D. 700
E. 750
Scanning our answer choices we want to find the number that contains a large prime factor. Thus, considering answer choice C, we have:

620 = 62 x 10 = 31 x 2 x 2 x 5

The sum is 31 + 5 + 2 + 2 = 40.

Answer: C

Scott Woodbury-Stewart
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