GMAT Question of the Day – DS Puzzle – May 1st, 2014
If x and y are integers, what is the value of x?
(1) (x – y)(x + y) = 15
(2) x/y > 0
[spoiler]E.[/spoiler]
(1) Always convert difference of squares – X^2 – y^2 = 15. Now you know that the difference of two perfect squares is equal to 15. Make a chart with perfect squares starting from 1:
1
4
9
16
25
36
49
64
81
100
64-49 = 15. 16-1 = 15.This narrows things down quite a bit but also consider that even exponents hide negative numbers you should always consider that the sign of the variable is hidden. x could be 8, -8, 4, -4 Insufficient.
(2) This only tells us that x, y are both positive or both negative. Insufficient.
(1) + (2) even together x could be 8, -8, 4, -4 Insufficient.