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How many factors of 42 are not factors of 56?

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by Brent@GMATPrepNow » Sat Dec 02, 2017 2:05 pm
swerve wrote:How many factors of 42 are not factors of 56?

A. 1
B. 2
C. 3
D. 4
E. 5
The fastest approach is probably to just list the factors of 42 and 56

Factors of 56: {1, 2, 4, 7, 8, 14, 28, 56}
Factors of 42: {1, 2, 3, 6, 7, 14, 21, 42}

So, the factors of 42 that are NOT factors of 56 are: 3, 6, 21 and 42 (four numbers in total)

Answer: D

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Brent
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by Scott@TargetTestPrep » Sun Sep 29, 2019 6:19 pm
swerve wrote:How many factors of 42 are not factors of 56?

A. 1
B. 2
C. 3
D. 4
E. 5

The OA is D.

Experts, how can I solve this PS question? I don't have it clear. Thanks.
42 = 2 x 3 x 7

56 = 7 x 8 = 7 x 2^3

So, the factors of 42 that are not of 56 are 3, 3 x 2, 3 x 7, and 2 x 3 x 7.

Answer: D

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