Is XY^2 St1: X Y+5 St2: X^2 - Y^2 = 0

Question

Is X>Y^2
St1: X > Y+5
St2: X^2 - Y^2 = 0

ywilfred · Answer

St1: x > y+5
y could be 1, x could be >6 (i.e. 7,8,9,10 etc)

y^2 = 1, x could be 7 and up so x>y^2

But if y=10, x = 16 and up
So now x may or may not be > y^2 = 100

Not sufficient.

St2: (x+y)(x-y)=0, so x=y, or x=-y

If x=y, is y>y+5? No. 
If x=-y, is -y>y+5? No.

We can answer the question for both values of x, so (2) is sufficient.

B it is.

ssap · Answer

Stmt 1:
If y = 1, x > 6
=> x > y^2 

If y= - 4, x > 1
Cannot conclude if x > 16 
=> Not suff

Stmt 2:
x^2 - y^2 = 0
=> x= y & x = - y
In either case x is not greater than y^2
=> Suff.

Ans = 'B'

christoph · Answer

what if x and y are a fraction ? i chose E) !

thearch · Answer

-y>y+5
If y=-3 then -(-3)>-3+5 (so answer is YES)
Am I missing something?
If I'm right, ans should be C

ssap · Answer

That's true - if x & y are fractions,
Stmt 2 is not suff.

Stmt 1& 2 together are suf.
x = y, -y
Applying this in Stmt 1, for this eqn to be true, y shld be -ve and |y| > 2.5
Hence, x > y2 will be false.
Ans is "C"

gmat_prep pl. post the solution.

christoph · Answer

1) + 2) is also insuff because...

1) states x>y+5 => x-y>5 => means x+y = 0 => x is +ve and y is -ve => insert x=3 and y=-3 => x<y^2 but x=1/2 and y=-1/2 x>y^2 => so C) is insuff

ssap · Answer

IF you use x= 1/2 & y= -(1/2),
then how will you validate Stmt 1 ??
Stmt 1: X > Y+5 
=>x > -(1/2) + 5 => x> 4.5 => invalid as u've assumed x=1/2.
In order for this stmt to be valid (here you're not proving validity of Stmt 1. You're accepting it to be true & valid) y has to be -ve with a magnitude >2.5
Now for values of x = -y as per above conditions, x<y^2

Stmt 1 & 2 are suff.

christoph · Answer

right! my mistake...i switch to C)

twixt · Answer

I am still stuck on C.

x= y^2 and x=y+5 intersect so statement 1 is not enough.

for statement 2 either x=y or x=-y, but in the only case of values within the -1 ...1 range inequality would be ok, so not enough.

the two statements together : in this -1...1 range, y+5 > y^2 so we can conclude.

HongHu · Answer

Question: Y^2-x<0? (1) Y^2-x(y+5)^2 10y+25<0 y<-5/2 If x=y then Y^2-x=y^2-y=y(y-1)>0 (y<0, y-1<0) If x=-y then Y^2-x=y^2+y=y(y+1)>0 (since y<-5/2 =>y+1<13/2<0) Sufficient (C)

HongHu · Answer

-y>y+5 means -2y>5. You can't answer "No" without knowing what y is.

Is X>Y^2 St1: X > Y+5 St2: X^2 - Y^2 = 0

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