I would go with E again
Given: x^2 + y ^2 = 1
Q: Is x+y =1
Stmt I
xy = 0
Either x is 0 or y is 0 but not both since x^2 + y^2 = 1
x=-1 y=0 x+y not equal to 1
x=1 y=0 x+y = 1
INSUFF
Stmt II
y=0
x=-1 y=0 x+y not equal to 1
x=1 y=0 x+y = 1
Together:
x=-1 y=0 x+y not equal to 1
x=1 y=0 x+y = 1
Same examples used to save time..
Choose E
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X+Y=1
Source: Beat The GMAT — Data Sufficiency |
if x^2 + y^2 = 1
then by 1)
3 choices:
1) x=0, y <> 0 --> then y^2 = 1 --> y=+1 or -1 --> insuff
2) x<>0, y=0
3) x=0, y=0
by 2)
y=0 so x=+1 or -1 -->insuff
combined still don't know whether x=1 or -1 so insuff
E
then by 1)
3 choices:
1) x=0, y <> 0 --> then y^2 = 1 --> y=+1 or -1 --> insuff
2) x<>0, y=0
3) x=0, y=0
by 2)
y=0 so x=+1 or -1 -->insuff
combined still don't know whether x=1 or -1 so insuff
E
