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Re: GMAT Prep Pair

by logitech » Tue Nov 18, 2008 9:26 am
moneyman wrote:Is the Answer D ?
10c2= 45


you can first select one of the 10 kids: 10

then, one of the remaining 9 kids: 9

9x10 = 90 ways but remember , we are asked PAIRs so

John McCain and Sarah Palin is the same pair with Sarah Palin and John McCain

:lol: and they are both useless! :-)



so you divide this number into 2:

90/2 = 45
LGTCH
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by mals24 » Tue Nov 18, 2008 9:34 am
We have to select 2 students from 10 = 10C2 = 45
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by Irena » Tue Nov 18, 2008 2:19 pm
what function is 10c2?

Thanx!
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by mals24 » Tue Nov 18, 2008 2:22 pm
10C2 is combination. (permutation and combination).

10c2 = 10!/[2!*(10-2)!]--combination formula
= 10!/(2!*8!).
=10*9*8!/2*8!
=10*9/2
=9*5
=45

Hope its clear :)
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by Irena » Tue Nov 18, 2008 2:31 pm
Got it! Thanx!
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