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# If two of the four expressions

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VP
Joined: 18 May 2008
Posts: 1176
If two of the four expressions  [#permalink]

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13 Nov 2008, 03:24
Help!

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Manager
Joined: 30 Sep 2008
Posts: 111

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13 Nov 2008, 03:45
x^2 - (by)^2 = (x-by)(x+by)

The probability P1 to get (x-by) = 1/4 as only x-y satisfies
Once taking x-y out of the list, the probability P2 to get x + by is 2 out of 3 (x+y and x+5y)

P = P1 * P2 = 1/4 * 2/3 = 1/6
Senior Manager
Joined: 04 Aug 2008
Posts: 362

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13 Nov 2008, 07:22
to satisfy the condition x^2-y^2 we need to have this form (x-y)(x+y)

so... two expressions are in the form (x-y) and two (x+y)

so 2*2/4*3*2*1=4/24=1/6

this is a tricky one...
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Manager
Joined: 23 Jul 2008
Posts: 180

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13 Nov 2008, 12:25
pretty straight forward

to get product of the nature of x^2 - (by)^2 we need to pick both (x+y) and (x-y) from a total of 4 expressions

probability= 2/4*1/3=1/6
Director
Joined: 14 Aug 2007
Posts: 692

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13 Nov 2008, 20:13
1/4C2 = 1/6 ( 1 for choosing x+y, x-y)

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: GMATPREP-product &nbs [#permalink] 13 Nov 2008, 20:13
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# If two of the four expressions

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