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Permutations???

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Permutations??? [#permalink] New post 31 Aug 2008, 19:04
I am having problems with this question:

The US Senate consists of 100 senators, two from each state. A committee consisting of five senators is to be formed.

(a) How many different committees are possible?
(b) How many committees are possible if no state may have more than one senator on the committee?
(c) What’s the probability that no state will have both of its senators on a committee?

I think the first (a) should be: 100*99*98*97*96

But I'm not sure about (b) and (c). Help.
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Re: Permutations??? [#permalink] New post 31 Aug 2008, 20:21
kamilaak wrote:
I am having problems with this question:

The US Senate consists of 100 senators, two from each state. A committee consisting of five senators is to be formed.

(a) How many different committees are possible?
(b) How many committees are possible if no state may have more than one senator on the committee?
(c) What’s the probability that no state will have both of its senators on a committee?

I think the first (a) should be: 100*99*98*97*96

But I'm not sure about (b) and (c). Help.

a. 100c5 = (100x99x98x97x96x95!)/(5x4x3x2x1x95!) = 5x33x49x97x96
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Re: Permutations??? [#permalink] New post 31 Aug 2008, 20:36
well, let me try my luck..



2)if no state may have more than one senator on the committee ---->

if only 50 senators are available to form commitee , then 50c3 = 50*49*48/3*2*1 = 19600.

3) What’s the probability that no state will have both of its senators on a committee?---->
5/100*4/98*3/96*2/94*1/92= something im not interested in..
is the method ok??
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Re: Permutations??? [#permalink] New post 31 Aug 2008, 20:58
why 50C3?

Should it be 50C5? Since we have 5 person committee?
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Re: Permutations??? [#permalink] New post 31 Aug 2008, 22:14
kamilaak wrote:
I am having problems with this question:

The US Senate consists of 100 senators, two from each state. A committee consisting of five senators is to be formed.

(a) How many different committees are possible?
(b) How many committees are possible if no state may have more than one senator on the committee?
(c) What’s the probability that no state will have both of its senators on a committee?

I think the first (a) should be: 100*99*98*97*96

But I'm not sure about (b) and (c). Help.


a)
100C5
b)

= 100*98*96*94*92 /5!
(First we can chose any senator(100 ways)* (one senator already chosen and we can't chose another senator from the same state so 98 members left)*....)

c)

p = (100*98*96*94*92 /5! ) / 100C5

What is OA
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Last edited by x2suresh on 04 Sep 2008, 07:19, edited 1 time in total.
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Re: Permutations??? [#permalink] New post 31 Aug 2008, 23:01
oh!!, yes i meant 50c5..
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Re: Permutations??? [#permalink] New post 03 Sep 2008, 15:54
1) 100 C 5

2) 50 C 5 * (2 C 1)^5

3) 2)/1) i.e., 50 C 5 * (2 C 1)/100 C 5
Re: Permutations???   [#permalink] 03 Sep 2008, 15:54
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