OG - Quant Review - #125

[Carla]

Question:

If x is an integer and y = 3x + 2 , which if the following CANNOT be a divisor of y.


a)4
b)5
c)6
d)7
e)8

The answer is C.

I was able to come up with the equation (y-2) = 3x

From the 3x it seems that (y-2) must be some multiple of 3...

What I do not understand is how this related to which number can not be a divisor of y?

Some help on this would be great - this is a problem type that I find difficult.

Thanks so much!!

Carla

[GMAT 5/18]

Carla,

I am sure there are better ways to solve, but when I see a problem that states "which of the following CANNOT be a ...........", I immediately try to prove which ones can be.

So, let's throw in integers for x.

x = 1, means b) is out
x = 2, means e) is out
x = 3, means nothing
x = 4, means d) is out
x = 5, means nothing
x = 6, means a) is out

That leaves c).

It might seem that this took a while, but it took less than 2 minutes.

Hope this helps!

[Carla]

Thanks that is a much better method that what I was doing.. I should really get into the habit of testing out numbers.. your way is WAY faster than the one I was trying..

-Carla

[esledge]

Quick citation note: This is from the Official Guide for GMAT Quantitative Review. For copyright reasons, we must cite full source name.