Anyone Can Help Me Understand This Problem?

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kavehfa: Newbie | Next Rank: 10 Posts; Posts: 7; Joined: Sun Nov 28, 2010 8:17 pm

Anyone Can Help Me Understand This Problem?

by kavehfa » Sun Dec 05, 2010 6:35 pm

Hello Everybody,

I am new to this forum and I hope I am posting this problem in the right place. I would really appreciate it if anyone could help me to solve this problem and understand similar questions.

-If a club has 10 member and 3 are to be chosen to be delegates to a conference, what is the probability that Sara, a member of the club be one of the delegates?

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Source: Beat The GMAT — Problem Solving | Sun Dec 05, 2010 6:35 pm

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Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pm; Location: Milpitas, CA; Thanked: 447 times; Followed by:88 members

by Rahul@gurome » Sun Dec 05, 2010 6:46 pm

Solution:
Required probability is (total number of favorable outcomes)/(total number of all possible outcomes).
Total number of all possible outcomes is 10C3 = 120.
For calculating the total number of favorable outcomes, we need to note that Sara will always be one of the delegates. So we need to select the other 2. This can be done in 9C2 = 36 ways.
So required probability is 36/120 = 3/10

Rahul Lakhani
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kavehfa: Newbie | Next Rank: 10 Posts; Posts: 7; Joined: Sun Nov 28, 2010 8:17 pm

by kavehfa » Sun Dec 05, 2010 6:50 pm

Thanks a lot for the answer. Is there any way we can differentiate between permutation and combination when we see a question?

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GMAT/MBA Expert

Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pm; Location: Milpitas, CA; Thanked: 447 times; Followed by:88 members

by Rahul@gurome » Sun Dec 05, 2010 7:10 pm

Thanks a lot for the answer. Is there any way we can differentiate between permutation and combination when we see a question?

If the question is asking about arrangement, go for permutation and if the question is asking about selection where order does not matter, go for combination.
This particular problem is talking about selection of delegates.
Hence we use the combination concept.

Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)