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# Combinations

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Senior Manager
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Combinations [#permalink]  05 Feb 2009, 17:48
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Re: Combinations [#permalink]  05 Feb 2009, 18:46
axl_oz wrote:

10C3*10C3
= 10*9*8/(1*2*3) *10*9*8/(1*2*3)
= 120*120 = 14400
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Re: Combinations [#permalink]  05 Feb 2009, 22:01
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Re: Combinations [#permalink]  05 Feb 2009, 22:45
Ibodullo wrote:

10 - Republicans
10 - Democrates

Answ= No of Ways choose 3 R out of 10 R * No of Ways choose 3 D out of 10 D
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Re: Combinations [#permalink]  06 Feb 2009, 09:28
x2suresh wrote:
Ibodullo wrote:

10 - Republicans
10 - Democrates

Answ= No of Ways choose 3 R out of 10 R * No of Ways choose 3 D out of 10 D

why would be 10x9x8x10x9x8 wrong?
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tusharvk

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Re: Combinations [#permalink]  06 Feb 2009, 10:01
tusharvk wrote:
x2suresh wrote:
Ibodullo wrote:

10 - Republicans
10 - Democrates

Answ= No of Ways choose 3 R out of 10 R * No of Ways choose 3 D out of 10 D

why would be 10x9x8x10x9x8 wrong?

You are using Permutations.. that's valid if order matters..

e.g. consider you have group of 3 repuplicans.. R1 R2 R3
how many ways you will select 2 Repulicans out of 3
Is it 3P2 or 3C2??? will see..

A1 A2 --A2 A1 <duplicate>
A2 A3 --A3 A2 <duplicate>
A3 A1 --A1 A3 <duplicate>

My answer = 3C2 = 3*2/2! = 3 ways.
A1 A2 =A2 A1
A2 A3 =A3 A2
A3 A1 =A1 A3

Did you get it
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Re: Combinations [#permalink]  06 Feb 2009, 11:08
axl_oz wrote:

The question clearly says combination. so permutation doesnot aapply to this case.

No of ways the cgroup can be made = 10c3 x 10c3 = 14,400
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Re: Combinations   [#permalink] 06 Feb 2009, 11:08
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