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Probability query

This topic has 1 expert reply and 0 member replies
prernamalhotra Senior | Next Rank: 100 Posts Default Avatar
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Probability query

Post Tue May 13, 2014 12:08 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Hi,

    Can you please help with the below mentioned problem:

    A certain university will select 1 of 7 candidates eligible to fill a position in mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in computer science department. If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?

    A) 42
    B) 70
    C) 140
    D) 160
    E) 315


    Thank you,
    Prerna

    Thanked by: mathrupradeep
    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    Post Tue May 13, 2014 12:51 am
    prernamalhotra wrote:
    A certain university will select 1 of 7 candidates eligible to fill a position in mathematics department and 2 of 10 candidates eligible to fill 2 identical positions in computer science department. If none of the candidates is eligible for a position in both departments, how many different sets of 3 candidates are there to fill the 3 positions?

    A) 42
    B) 70
    C) 140
    D) 160
    E) 315

    We can take the task of filling both positions and break it into stages.

    Stage 1: Fill the 1 math position
    There are 7 candidates, so we can complete stage 1 in 7 ways

    Stage 2: Fill the 2 computer science positions
    Note that the order in which we select candidates doesn't matter. For example, selecting candidate B and then candidate C is the same as selecting candidate C and then candidate B. So, we can use combinations here.
    We can select 2 candidates from 10 in 10C2 ways (= 45 ways)

    Aside: If anyone is interested, we have a free video on calculating combinations (like 10C2) in your head: http://www.gmatprepnow.com/module/gmat-counting?id=789

    By the Fundamental Counting Principle (FCP), we can complete the two stages (and thus fill the three positions in (7)(45) ways (= 315 ways)

    Answer: E
    --------------------------

    Note: the FCP can be used to solve the majority of counting questions on the GMAT. For more information about the FCP, watch our free video: http://www.gmatprepnow.com/module/gmat-counting?id=775

    Then you can try solving the following questions:

    EASY
    - http://www.beatthegmat.com/what-should-be-the-answer-t267256.html
    - http://www.beatthegmat.com/counting-problem-company-recruitment-t244302.html
    - http://www.beatthegmat.com/picking-a-5-digit-code-with-an-odd-middle-digit-t273110.html
    - http://www.beatthegmat.com/permutation-combination-simple-one-t257412.html
    - http://www.beatthegmat.com/simple-one-t270061.html
    - http://www.beatthegmat.com/mouse-pellets-t274303.html


    MEDIUM
    - http://www.beatthegmat.com/combinatorics-solution-explanation-t273194.html
    - http://www.beatthegmat.com/arabian-horses-good-one-t150703.html
    - http://www.beatthegmat.com/sub-sets-probability-t273337.html
    - http://www.beatthegmat.com/combinatorics-problem-t273180.html
    - http://www.beatthegmat.com/digits-numbers-t270127.html
    - http://www.beatthegmat.com/doubt-on-separator-method-t271047.html
    - http://www.beatthegmat.com/combinatorics-problem-t267079.html


    DIFFICULT
    - http://www.beatthegmat.com/wonderful-p-c-ques-t271001.html
    - http://www.beatthegmat.com/ps-counting-t273659.html
    - http://www.beatthegmat.com/permutation-and-combination-t273915.html
    - http://www.beatthegmat.com/please-solve-this-real-gmat-quant-question-t271499.html
    - http://www.beatthegmat.com/no-two-ladies-sit-together-t275661.html
    - http://www.beatthegmat.com/laniera-s-construction-company-is-offering-home-buyers-a-wi-t215764.html

    Cheers,
    Brent

    _________________
    Brent Hanneson – Founder of GMATPrepNow.com
    Use our video course along with Beat The GMAT's free 60-Day Study Guide

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    Thanked by: prernamalhotra
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