Source: Official Guide for the GMAT 13th Ed. Data Sufficiency; #173 Official Guide for the GMAT 2015 14th Ed. Data Sufficiency; #173


If x, y, and z are positive

If x, y, and z are positive integers, is x-y odd?

2 Explanations


anish shah

Hi mike , if we simply put the equation x -y = z^2 -z^2 +2z-1 in play it will also lead to odd number only.. Also you should display the official guide solutions on the home page or somewhere visible..found this gold mine accidentally but would have been lot of help at the start of my prep

Sep 22, 2015 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Anish,
Yes, you're correct! If we plug in z^2 for x and (z-1)^2 for y into the expression x-y, we end up with 2z-1 after simplifying. The expression 2z-1 will be odd regardless of whether z is even or odd, so we can definitely say that x-y will be odd given the conditions in statements I and II :)
I'm happy to hear that you've found our explanations on the official material useful :D However, I'm sorry that you did not know about them as you began studying. We have tried to make them as accessible as possible by creating our GMAT forum, where we have links to all of Magoosh's video explanations for official GMAT material. We are always working to improve, though. Thanks for your feedback :)

Oct 31, 2015 • Reply


Gravatar Mike McGarry, Magoosh Tutor

Jan 5, 2014 • Comment

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