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by hey_thr67 » Sun May 20, 2012 10:27 pm
A 10-member student leadership committee consists of juniors and seniors. Exactly 6 students will be selected from this group to attend a national convention. What is the probability that at least 3 seniors are selected for the committee?

1- 1/10
2- 3/10
3- 3/5
4-6/7
5-13/14
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Source: — Problem Solving |

by LalaB » Sun May 20, 2012 10:51 pm
It seems that this quesiton is incomplete.nowhere is mentioned how many seniors and juniors are in this 10 member committee
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by hey_thr67 » Sun May 20, 2012 10:59 pm
Oh my....

restating the question:

A 10-member student leadership committee consists of juniors and seniors. There are 4 junior and 6 senior students. Exactly 6 students will be selected from this group to attend a national convention. What is the probability that at least 3 seniors are selected for the committee?

1- 1/10
2- 3/10
3- 3/5
4-6/7
5-13/14
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by Anurag@Gurome » Sun May 20, 2012 11:11 pm
hey_thr67 wrote:Oh my....

restating the question:

A 10-member student leadership committee consists of juniors and seniors. There are 4 junior and 6 senior students. Exactly 6 students will be selected from this group to attend a national convention. What is the probability that at least 3 seniors are selected for the committee?

1- 1/10
2- 3/10
3- 3/5
4-6/7
5-13/14
Seniors = 6, Juniors = 4
Possible combinations are (3S, 3J), (4S, 2J), (5S, 1J), (6S, 0J)
Number of ways in which at least 3 seniors are selected for the committee = (6C3 * 4C3) + (6C4 * 4C2) + (6C5 * 4C1) + (6C6 * 4C0)
= (20 * 4) + (15 * 6) + (6 * 4) + (1)
= 195
Number of ways of choosing 6 students from 10 = 10C6 = (10 * 9 * 8 * 7)/(4 * 3 * 2) = 10 * 3 * 7 = 210
Required probability = 195/210 = [spoiler]13/14[/spoiler]

The correct answer is E.[/spoiler]
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by LalaB » Sun May 20, 2012 11:31 pm
at least 3 seniors=1 -(less than 3 seniors)

please pay attention that less than 3 seniors option is true, only if -

S S J J J J

u cant have less than that,since u have 4 Juniors at most

so 1- (6!/2!*4!)/(10!/6!*4!)=195/210=13/14
Happy are those who dream dreams and are ready to pay the price to make them come true.(c)

In order to succeed, your desire for success should be greater than your fear of failure.(c)
Join the discussion