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Re: If xy = – 6, what is the value of xy(x + y)? (1) x – y = 5 [#permalink]
27 Apr 2012, 09:48

1

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Expert's post

If xy = – 6, what is the value of xy(x + y)?

(1) x-y=5 --> x=y+5 --> xy=(y+5)y=-6 --> y^2+5y+6=0 --> y=-3 or y=-2. If y=-3 then x=y+5=2 so xy(x+y)=-6(x+y)=6. But if y=-2 then x=y+5=3 so xy(x+y)=-6(x+y)=-6. Two different answers, hence not sufficient.

Re: If xy = – 6, what is the value of xy(x + y)? (1) x – y = 5 [#permalink]
27 Apr 2012, 09:52

Bunuel wrote:

If xy = – 6, what is the value of xy(x + y)?

(1) x-y=5 --> x=y+5 --> xy=(y+5)y=-6 --> y^2+5y+6=0 --> y=-3 or y=-2. If y=-3 then x=y+5=2 so xy(x+y)=-6(x+y)=6. But if y=-2 then x=y+5=3 so xy(x+y)=-6(x+y)=-6. Two different answers, hence not sufficient.

Re: If xy = -6 , what is the value of xy(x+y ) [#permalink]
14 Feb 2013, 08:39

Expert's post

roopika2990 wrote:

If xy = -6 , what is the value of xy(x+y ) ? (1) x – y = 5 (2)xy^2 = 48

xy=-6 ----> x=-6/y

S1) x-y=5 ---------------> x=y+5 -------------> -6/y=y+5 --------> y^2 + 5y + 6 = 0 -------> y = -3 or -2 two values for y so not sufficiesnt

S2) xy^2 = 48 -------> We know x=-6/y -------> therefore (-6/y)(y^2)=48 -------> -6y = 48 -------> y = -8 and x = 6/8 so now we can calculate the value of xy(x+y) hence statement is sufficient