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What is the value of (x - y)^4? (1) The product of x and y

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Senior Manager
Joined: 10 Mar 2008
Posts: 355
What is the value of (x - y)^4? (1) The product of x and y [#permalink]

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29 Sep 2008, 08:31
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What is the value of (x - y)^4?
(1) The product of x and y is 7.
(2) x and y are integers.
VP
Joined: 05 Jul 2008
Posts: 1401

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29 Sep 2008, 08:43
vksunder wrote:
What is the value of (x - y)^4?
(1) The product of x and y is 7.
(2) x and y are integers.

C

xy=7 means there are many pairs satisfying (1,7) (7,1) (7/2,2) (3,7/3) and so on. Insuff

x,y are integers means infinite number of pairs will satisfy such condition and hence infinite values. Insuff

Together eliminate every thing else other than (1,7) and (7,1) Both result in same value. Hence C
Director
Joined: 12 Jul 2008
Posts: 514
Schools: Wharton

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29 Sep 2008, 08:43
vksunder wrote:
What is the value of (x - y)^4?
(1) The product of x and y is 7.
(2) x and y are integers.

(1) Insufficient

If x = y = sqrt(7), (x-y)^4 = 0
If x = 7, y = 1, (x-y)^4 = 6^4

(2) Insufficient

x and y could be any integer

(1) and (2) Sufficient

Because 7 is a prime number, x and y are 1 and 7 or vice versa.
Thus, x - y = 6 or -6
6^4 = (-6)^4
Therefore, we know that (x-y)^4
Re: exponents   [#permalink] 29 Sep 2008, 08:43
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What is the value of (x - y)^4? (1) The product of x and y

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