Algebra

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pareekbharat86: Master | Next Rank: 500 Posts; Posts: 168; Joined: Thu Nov 01, 2012 7:43 pm; Thanked: 1 times

by pareekbharat86 » Sat Nov 02, 2013 5:18 am

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

(1) x - y=5
(2) x*y*y = 18

OA is B.

Source- GMAT Practice Tests (Test Code 25)

Thanks,
Bharat.

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Source: Beat The GMAT — Data Sufficiency | Sat Nov 02, 2013 5:18 am

mevicks: Master | Next Rank: 500 Posts; Posts: 269; Joined: Thu Sep 19, 2013 12:46 amFollowed by: 7 members; Thanked: 94 times

by mevicks » Sat Nov 02, 2013 5:49 am

pareekbharat86 wrote:If xy = -6,what is the value of xy*(x + y)?
(1) x - y = 5
(2) x*y*y = 18

Given: xy = -6

Q: xy*(x + y) = ?

St1:
x - y = 5
x = 5 + y
substituting : xy = -6 --> (y + 5)*y = -6
yÂ² + 5y + 6 = 0
y = -3 or y = -2
The value of x would change accordingly, Indefinite answer; INSUFFICIENT

St2:
x*y*y = 18
xy = -6
Substituting xy in the above equation we can find out the value of y and thus the value of x.

The target question can be answered by finding out the values of x & y, SUFFICIENT

Answer B

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