Source: Revised GRE PDF 1st Ed. Section 5: Math; #22 (p. 79)

11

If c and d are positive integers

If c and d are positive integers and m is the greatest common factor of c and d, then m must be the greatest common factor of c and which of the following integers? c+d, 2+d, cd, 2d, d^2

2 Explanations

1

Megashree R

I did not understand how Chris chose those numbers logically. Can you please explain further?

Sep 30, 2016 • Comment

Sam Kinsman, Magoosh Tutor

Hi Megashree,

To solve this problem, Chris chose the following numbers:

c=8
d=4
m=4

Chris chose these numbers because they satisfy what the question told us ("c and d are positive integers and m is the greatest common factor of c and d"), and they are relatively small, which means they are easy to work with.

Those are the two things you should think about when you're choosing numbers for variables: you should make sure that the numbers satisfy what the question tells us, and that the numbers are easy to work with. Also, you should avoid picking the numbers 1 and 0, since they tend to behave a bit differently than other numbers do.

Oct 4, 2016 • Reply

2

Gravatar Chris Lele, Magoosh Tutor

Sep 25, 2012 • Comment

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