Can anyone help solving this ... (x-y)^4

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imane81: Senior | Next Rank: 100 Posts; Posts: 40; Joined: Wed Jan 13, 2010 7:17 pmFollowed by: 1 member; Thanked: 1 times

by imane81 » Thu Jan 21, 2010 3:14 pm

What is the value of (x - y)^4?
(1)The product of x and y is 7.
(2)x and y are integers.

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

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Source: Beat The GMAT — Data Sufficiency | Thu Jan 21, 2010 3:14 pm

apuso: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Mon Jan 18, 2010 8:27 pm; Thanked: 1 times

by apuso » Thu Jan 21, 2010 7:23 pm

(A)

since 7 is a prime number thus if x*y has to be 7 then its either x and y are 1 & 7 or -1 & -7...but in either of the cases the value of (x - y)^4 can be derived and would be the same.

whats the OA.

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aakar: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Wed Sep 02, 2009 6:06 am; Thanked: 1 times

by aakar » Fri Jan 22, 2010 9:45 am

Has to be (C).

Statement I only tells you that XY = 7, but doesn't tell you that X and Y are integers as such X = 49 and Y = 1/7, X = 1/3 Y = 21 etc..

Statement II only tells you that X and Y are integers, not suff...

Both together tell you that X and Y are either 1, 7 or 7,1 or -1, -7 or -7, -1. In all cases x-y will give you 6 or -6, raised to the fourth give you the same answer...

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mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Fri Jan 22, 2010 6:51 pm

Answer should be C

Statement 1 - x = 7, y = 1, or x = -7, y = -1, or x = 49, y = 1/7 satisfy the statement
Statement 2 - this tells us nothing but x and y are integers, they could be any integer

combining the statements - we get x = 7, y = 1 and x = -7, y = -1, but (x - y)^4 will have the same value irrespective of sign of x and y.

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thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Sat Jan 23, 2010 12:11 am

apuso wrote:(A)

since 7 is a prime number thus if x*y has to be 7 then its either x and y are 1 & 7 or -1 & -7...but in either of the cases the value of (x - y)^4 can be derived and would be the same.

whats the OA.

but s1) never tells that x and y are int it can be 7/5*5 ; 7/2*2 ;7/3*3 and so on

it has to be C

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lalmanistl: Junior | Next Rank: 30 Posts; Posts: 13; Joined: Wed Oct 01, 2008 4:41 pm; Location: USA

by lalmanistl » Mon Jan 25, 2010 4:07 pm

I agree C is the answer.

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