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naveenhv
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Permutation and Combination

by naveenhv Fri May 06, 2011 1:40 pm

What is the number of different committees of 4 people that can be selected from a group of 10 people?

a) 20

b) 40

c) 80

d) 120

e) 210
vikram4689
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Re: Permutation and Combination

by vikram4689 Sat May 07, 2011 4:52 am

This is a direct question of Combinatons.
C (n,r) = n ! / [ r ! * (n! - r !) ]

n = total no of entities = 10 (here)
r = no of entities to be selected = 4 (here)

solve by substituting the values. Answer is 210, e)
jnelson0612
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Re: Permutation and Combination

by jnelson0612 Sat May 07, 2011 4:20 pm

vikram4689 Wrote:This is a direct question of Combinatons.
C (n,r) = n ! / [ r ! * (n! - r !) ]

n = total no of entities = 10 (here)
r = no of entities to be selected = 4 (here)

solve by substituting the values. Answer is 210, e)


Correct. I use the formula:

Pool!
In! Out!

It yields the same numbers as the formula above, but I think it's easier to use (or at least it is for me). In this case it would be:
10!
4! 6!
Jamie Nelson
ManhattanGMAT Instructor