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# (Please solve this problem of you can!) PS Problem #2. Thx!

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Intern
Joined: 23 Jun 2009
Posts: 47
(Please solve this problem of you can!) PS Problem #2. Thx! [#permalink]

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24 Jul 2009, 13:39
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If two of the four expressions x+y, x+5y, x-y, and 5x-y are chosen at random, what is the probability that their product will be in the form x^2 - (by)^2, where b is an integer?

Thanks a lot;...greatly appreciated.
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Joined: 20 Jul 2009
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Location: Africa/Europe
Schools: Kellogg; Ross ($$); Tuck Re: (Please solve this problem of you can!) PS Problem #2. Thx! [#permalink] ### Show Tags 24 Jul 2009, 13:50 could you provide the answer for this one? I think 3/8 could explain if its correct. Intern Joined: 23 Jun 2009 Posts: 47 Re: (Please solve this problem of you can!) PS Problem #2. Thx! [#permalink] ### Show Tags 24 Jul 2009, 13:58 uzonwagba wrote: If two of the four expressions x+y, x+5y, x-y, and 5x-y are chosen at random, what is the probability that their product will be in the form x^2 - (by)^2, where b is an integer? Thanks a lot;...greatly appreciated. The options are A) 1/2 B) 1/3 C) 1/4 D) 1/5 E) 1/6 Manager Joined: 18 Jul 2009 Posts: 169 Location: India Schools: South Asian B-schools Re: (Please solve this problem of you can!) PS Problem #2. Thx! [#permalink] ### Show Tags 24 Jul 2009, 14:12 I think ans is 1/6 ; plz somone confirm x^2 - (by)^2 = (x+by)(x-by) .. we will try to fit our multiplication in this form; From the above given choices x+y, x+5y, x-y, and 5x-y (x+y) (x-y) is the only choice possible out of 4C2 choices ; hence ans is 1 out of 6. _________________ Bhushan S. If you like my post....Consider it for Kudos Current Student Affiliations: ? Joined: 20 Jul 2009 Posts: 191 Location: Africa/Europe Schools: Kellogg; Ross ($$); Tuck
Re: (Please solve this problem of you can!) PS Problem #2. Thx! [#permalink]

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24 Jul 2009, 14:22
bhushan252 wrote:
I think ans is 1/6 ; plz somone confirm

x^2 - (by)^2 = (x+by)(x-by) .. we will try to fit our multiplication in this form; From the above given choices x+y, x+5y, x-y, and 5x-y

(x+y) (x-y) is the only choice possible out of 4C2 choices ; hence ans is 1 out of 6.

agree...
I was thinking of expression in form of x²-by² instead of x²-(by)²
Intern
Joined: 23 Jun 2009
Posts: 47
Re: (Please solve this problem of you can!) PS Problem #2. Thx! [#permalink]

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24 Jul 2009, 22:57
Yes; thanks a lot.

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Re: (Please solve this problem of you can!) PS Problem #2. Thx!   [#permalink] 24 Jul 2009, 22:57
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