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# Out of 8 employees including Bob and Mary, a team of 4

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Senior Manager
Joined: 04 Mar 2007
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Out of 8 employees including Bob and Mary, a team of 4 [#permalink]

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12 May 2007, 04:18
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Out of 8 employees including Bob and Mary, a team of 4 members is to be selected at random. What is the probability that the team will include Mary but exclude Bob?
Manager
Joined: 02 Jan 2007
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12 May 2007, 04:33
Senior Manager
Joined: 04 Mar 2007
Posts: 440
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Kudos [?]: 31 [0], given: 0

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12 May 2007, 04:34
Thanks.
Didn't find it somehow in my search.
Manager
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12 May 2007, 04:44
Happens to me all the time .
You seem to be focusing on Perms/Combs & Probability these days.
Are you also using Project GMAT?
Senior Manager
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12 May 2007, 04:50
No, I don't.
I am just going through the problems which I didn't understand earlier. They are from different GMAT sources.
Yeah, you are right. Combinatorix and probabilities are the hardest topics for me.
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13 May 2007, 10:02
I believe the probability is 2/7. Start with the prob of getting Mary on the team: 1/8 but you have four shots of getting her on the team since you are picking 4 team members, so this results in 1/2 chance of getting Mary on the team. Next the chance of not getting Bob in the 2nd spot is 6/7, because there are 7 members to choose and from and 1 who we don't want: Bob. Likewise the chance of not getting Bob on the 3rd and 4th selection are 5/6 and 4/5 respectively. This multiplies out to 2/7.
Probability of Selected Team   [#permalink] 13 May 2007, 10:02
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