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# What is the value of (x - y)^4?

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What is the value of (x - y)^4? [#permalink]

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22 Jun 2008, 05:44
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62% (00:44) correct 38% (00:51) wrong based on 249 sessions

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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

OPEN DISCUSSION OF THIS QUESTION IS HERE: what-is-the-value-of-x-y-128238.html
[Reveal] Spoiler: OA

Last edited by Bunuel on 16 Jun 2015, 07:50, edited 1 time in total.
Renamed the topic, edited the question and added the OA.

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Re: What is the value of (x - y)^4? [#permalink]

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22 Jun 2008, 06:07
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looks to be C

(x-y)^4?

xy=7..ok, well if x=7 y=1.. you get 6^4..

or you could have x=14 y=1/2 then 13.5^4..isnuff

2) is clearly insuff

together..

xy=7..x and y integers..we know 7 is a prime..so x=7 y=1 or y=7 x=1..either way ans is 6^4

C it is.

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Re: What is the value of (x - y)^4? [#permalink]

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22 Jun 2008, 06:11
ritula wrote:
What is the value of (x - y)^4?
(1) The product of x and y is 7.
(2) x and y are integers.

Should be C. If x and y are integers and the product of x and y is 7 then we can determine the value of x and y...which is either 1 and 7 or 7 and 1. Both cases generate same value of (x-y)^4, which is 6^4.

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Re: What is the value of (x - y)^4? [#permalink]

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22 Jun 2008, 10:20
The key is that product is a prime number...makes our life easier...Only way to have a product 7 is x=7, y=1 or x=1, y = 7 when both are integers...

Also, an even power for x-y makes it a C....for any off power of x-y, this would have been E, as you will get a positive and a negative solution...

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Re: What is the value of (x - y)^4? [#permalink]

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22 Jun 2008, 22:25
yes OA is C indeed. thanks !

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Re: What is the value of (x - y)^4? [#permalink]

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22 Jun 2008, 23:06
Also do not ignore the fact that x and y can be negative (-1 and -7 or -7 and -1). In either case, the answer will be C.

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Re: What is the value of (x - y)^4? [#permalink]

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09 Dec 2009, 08:40
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Statement 1 ---------------Insufficient

X can be 7 when Y is 1 or X can be 1/7 when Y is 7 and so on……

Statement 2 --------------CLEARLY INSUFFICIENT (No info about the numbers)

Combining the two,

Since they are both integers and 7 happens to be a prime number divisible by 1 and 7 only, the numbers are 7 and 1

Whether y is 7 or 1 (Same with x), does not matter as the power (4 in this case) is even which will give the same positive result

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Re: What is the value of (x - y)^4? [#permalink]

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18 Sep 2011, 02:32
i have to say nice question..totally deceive me....

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Re: What is the value of (x - y)^4? [#permalink]

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18 Sep 2011, 20:15
Looks like a straight C.

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Re: What is the value of (x - y)^4? [#permalink]

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16 Jun 2015, 07:15
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: What is the value of (x - y)^4? [#permalink]

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16 Jun 2015, 07:51
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What is the value of (x - y)^4?

(1) The product of x and y is 7, well this one is clearly insufficient: if $$x=7$$ and $$y=1$$ then $$(x-y)^4=6^4$$ and if $$x=14$$ and $$y=\frac{1}{2}$$ then $$(x-y)^4=(\frac{27}{2})^4$$, two different answers, hence not sufficient.

(2) x and y are integers. Also insufficient.

(1)+(2) As $$x$$ and $$y$$ are integers and $$xy=7$$ then either $$x$$ and $$y$$ are 1 and 7 (or vise-versa) or -1 and -7 (or vise-versa) in any case because of even power: $$(x-y)^4=(7-1)^4=(1-7)^4=(-7+1)^4=(-1+7)^4=6^4$$. Sufficient.

OPEN DISCUSSION OF THIS QUESTION IS HERE: what-is-the-value-of-x-y-128238.html
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Re: What is the value of (x - y)^4?   [#permalink] 16 Jun 2015, 07:51
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