GWD-17-09

[Msmistake]

我找不到這一題
如果有重複的....請見諒

Data Sufficiency

Is x greater than y

1) x-y^2>0
2) xy<0

Ans: C

為什麼 A 不對, 光從 X > Y^2 不足夠嗎?

[eced]

因為沒說x,y是整數
若y^2=1/4 , y=1/2 , x=1/3 . x>y^2,但x<y

[Msmistake]

那 xy<0 又有什麼作用呢?

even y=1/2 x=1/3 xy還是>0
爲什麼 A+B 可以得到答案?

[vantreal]

(1) x-y^2>0
cannot be determined
(reasons given by eced) ---> insufficient

(2) xy< 0
there are two cases.
a. x>0, y<0
b. x<0, y>0
still cannot determine x or y is greater than the other --> insufficient

(1) +(2)

from (1)
x-y^2>0
any number 的square must > 0
x- a positive number>0
which means x>0

go to (2)
x>0, then it must be case a).
x>0, y<0 --> sufficient

Ans: C