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Combination: differences

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by rah_pandey » Mon Jun 15, 2009 7:59 am
Are you sure according to me it should be 19.
by differences you mean (x-y) where x,y belong to {2,3,5,10,15}
in any case no of differences cannot be greater than (5c2)*(2!)+1
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Re: Combination: differences

by Stuart@KaplanGMAT » Mon Jun 15, 2009 11:33 am
Naruto wrote:How many different differences can be obtained by taking 2 numbers at a time from 2,3,5,10 and 15

A 49
B 1898
C 1440
D 4320
E 720

Please double check the question - as written, the answer should be 18.

(5 numbers can be chosen first, 4 numbers can be chosen second, so there are 5*4 = 20 differences; however, 15-10 gives the same result as 10-5 and 5-10 gives the same result as 10-15, so we have to subtract the two duplicates.)
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by rah_pandey » Mon Jun 15, 2009 7:38 pm
I think difference of a no from itself can also be taken as part of the soln that makes it 18+1=19
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by tohellandback » Mon Jun 15, 2009 10:21 pm
according to me its 19
the differences are:

(2,2),(2,3),(2,5),(2,10),(2,15),(3,5),(3,10),(3,15),(5,10),(5,15),(3,2),(5,2),(10,2)(15,2),(5,3),(10,3),(15,3),(10,5),(15,5)
The powers of two are bloody impolite!!
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by Naruto » Mon Jun 15, 2009 10:38 pm
Yes even my answer was 19, I was wondering if i was reading the question wrong or something, am sorry guys I got this question from one of the online prep tests and i guess they are no good and have wrong answers. I'll be more careful of my posts henceforth.

:oops:
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