x-y

[heshamelaziry]

Does x-y = 200 ?

(1) x=10^2
(2) x=100 and y=-100


Seems very easy, don't understand why choice 1 is incorrect ?

[tohellandback]

well,
1 says nothing about Y . thats why 1 is incorrect
for y=-100, x-y will be 200
for y=any other value it x-y will not be 200. Thats why NOT SUFF

2) is SUFF

[grockit_jake]

Without an explanation for y, you can't know x - y. (1) is not sufficient because you are missing information on how to find y.