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Re: What is the value of x ? [#permalink]
29 Feb 2012, 23:59

2

This post received KUDOS

Expert's post

What is the value of x ?

(1) x^2 + y^2 = 25. Two unknowns, hence can not get the value of x. Not sufficient. (2) xy = 12. Two unknowns, hence can not get the value of x. Not sufficient.

(1)+(2) Now, we can go strictly algebraic way, though I'd suggest the following: x^2 + y^2 = 5^2 always makes me think about Pythagorean triple (3, 4, 5): 3^2+4^2=5^2. Now, 3 and 4 fit perfectly in xy = 12 too, so x can be 3 or 4. Moreover if we take the sign into consideration then there are even more options for (x, y): (3, 4); (4, 3); (-3, -4); (-4, -3). So, we have 4 possible values of x. Not sufficient.

Re: What is the value of x ? [#permalink]
01 Mar 2012, 07:58

Expert's post

GMATD11 wrote:

x=? a) x^2 + y^2 = 25 x^2+ y^2 = 5^2 but we cannot deduce value of x ---NS

b) x*y = 12 Clearly not sufficient

a+b) x^2+y^2+2xy= (x+y)^2

25+24= (x+y)^2 7 = x+y need y to calculate X --NS E

From (x+y)^2=49 --> x+y=7 or x+y=-7. Also, the point is not that we need y to calculate x, but that we can get 4 different values of y from this system of equation, which give 4 different values of x. _________________

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