Combinatorics (selection of candidates) : GMAT Quantitative Section
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# Combinatorics (selection of candidates)

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Intern
Joined: 06 Jun 2012
Posts: 7
GMAT Date: 10-16-2013
WE: Project Management (Health Care)
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20 Jul 2013, 22:40
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I am making up a question myself. But i dont know how to solve the question mathematically. Can some one help. The question is as below.

A company wants to select 2 candidates from one college (Example: ISB) AND one from any other college (i.e. NON-ISB, example Harvard OR Insead).
The company chooses 2 out of 3 candidates from ISB and interviews only one candidate from Harvard and Insead each but chooses only one out of HARVARD OR INSEAD. How many possibilities exist to have 3 people chosen by the company.

So the grid can look like below:

2 ISB candidates chosen (From Candidate no. 1 OR Candidate no. 2 OR Candidate no. 3) AND 1 NON-ISB chosen (From Candidate no. 1 - Harvard OR Candidate no. 1 - Insead)

When i did the question through the long route of combinations I get 6 possibilities. Let me know if i am right and how to solve this question mathematically?
Veritas Prep GMAT Instructor
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Re: Combinatorics (selection of candidates) [#permalink]

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22 Jul 2013, 20:35
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Expert's post
Phali wrote:
I am making up a question myself. But i dont know how to solve the question mathematically. Can some one help. The question is as below.

A company wants to select 2 candidates from one college (Example: ISB) AND one from any other college (i.e. NON-ISB, example Harvard OR Insead).
The company chooses 2 out of 3 candidates from ISB and interviews only one candidate from Harvard and Insead each but chooses only one out of HARVARD OR INSEAD. How many possibilities exist to have 3 people chosen by the company.

So the grid can look like below:

2 ISB candidates chosen (From Candidate no. 1 OR Candidate no. 2 OR Candidate no. 3) AND 1 NON-ISB chosen (From Candidate no. 1 - Harvard OR Candidate no. 1 - Insead)

When i did the question through the long route of combinations I get 6 possibilities. Let me know if i am right and how to solve this question mathematically?

You have 3 people from ISB - you need to choose 2. You can do this in 3C2 = 3 ways. Or think that you have to drop one person out of 3. You can select that one person in 3 ways.
(Check out this post for the nCr formula: http://www.veritasprep.com/blog/2011/11 ... binations/)

Next, you need to choose 1 person from 2 non ISB. You can do this in 2 ways.

Total no of ways of selecting the 3 people = 3*2 = 6 (you multiply because both actions have to be done simultaneously. You must select 2 out of 3 ISB and 1 out of 2 non ISB)
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Re: Combinatorics (selection of candidates)   [#permalink] 22 Jul 2013, 20:35
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