DS - value - gmat prep

[ccassel]

I am overlooking something obvious here; can anyone explain the answer?

If wx = y, what is the value of xy?

1. wx^2 = 16
2. y = 4

Answer is A

Cheers,

[manpsingh87]

I am overlooking something obvious here; can anyone explain the answer?

If wx = y, what is the value of xy?

1. wx^2 = 16
2. y = 4

Answer is A

Cheers,

wx=y; xy??

1) wx^2= 16
wx^2 can be written as wx(x); also from question we know that wx=y;
hence yx=16 therefore one is sufficient.

2)y=4;

wx=4; w=1 x=4; therfore xy can be 16;
if w=x=2 then xy will be 2*4=8;
hence 2 alone is not sufficient to answer the question
hence A

[ccassel]

Due to fatigue, I jumped to the conclusion that wx^2= 16 = y^2 when in fact it is not equal.

Thanks for pointing out my mistake manpsingh87.

Cheers,

[GMATGuruNY]

If wx=y, what is the value of xy?

(1) w(x^2) = 16

(2) y = 4

An efficient approach -- one that doesn't require any algebraic insight -- would be to plug in two sets of values that satisfy the conditions given. If the value of xy stays the same, then the statement is sufficient. If the value of xy changes, then the statement is insufficient.

Statement 1: w(x^2) = 16
Let w=4, x=2, so that 4*(2^2) = 16.
Then y = wx = 4*2 = 8.
xy = 2*8 = 16.

Let w=16, x=1, so that 16*(1^2) = 16.
Then y = wx = 16*1 = 16.
xy = 1*16 = 16.

Since the value of xy stays the same, sufficient.

Statement 2: y=4
No way to determine the value of x.
Insufficient.

The correct answer is A.

[nirbans]

Can x be root 2 and w be 8?