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OG13 - Quant Review - DS - 49

This topic has 3 expert replies and 3 member replies
vittovangind Junior | Next Rank: 30 Posts
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OG13 - Quant Review - DS - 49

Post Sun Jan 19, 2014 2:06 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    Hello,

    "49. How many directors of both Company K and Company R?

    (1) Thee were 17 directors present at joint meeting of the directors of Company K and Company R, and no directors were absent.

    (2) Company K has 12 directors and Company R has 8 directors."

    Please could someone rephrase the solution taking (1) and (2) together. Specificall, I don't understand why the 3 peoples missing at the joint meeting must be joint directors.

    Many Thanks,

    Vitto[/list]

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    Post Sun Jan 19, 2014 4:24 pm
    Hi Vitto,

    This DS question is based on a variation of the "overlapping sets" concept that you'll likely see on the GMAT once or twice. There are several different ways to solve this problem, but since this is a simple variation, I'll show you the simple math.

    The idea is this: If a person is a member of BOTH groups, then that person has been "counted" twice (once for the first group and once for the second). When calculating the total number of people, you're NOT supposed to count people twice, so you have to mathematically remove that "second count."

    Here's a simple example:
    3 people total
    1 person in group A
    1 person in group B
    1 person in BOTH group A and B

    Total in group A = 2
    Total in group B = 2
    But that DOES NOT mean that there are 4 people; there are only 3.

    In this type of question, the "math" formula is Total = Group A + Group B - BOTH = 2 + 2 - 1 = 3 people total

    The same logic applies in this question.
    Total = 17
    Company K = 12
    Company R = 8
    Both = ?

    Total = CompK + CompR - BOTH
    17 = 12 + 8 - BOTH
    17 = 20 - BOTH
    3 = BOTH

    GMAT assassins aren't born, they're made,
    Rich

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    Thanked by: vittovangind

    GMAT/MBA Expert

    Post Tue Jan 21, 2014 1:46 pm
    The solution below is taken from the GMATFix App.

    ttp://www.youtube.com/watch?v=3Nk_np_H7fY" target="_blank">

    -Patrick

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    Thanked by: vittovangind
    Post Tue Jan 21, 2014 4:17 pm
    vittovangind wrote:
    Hello,

    How many directors of both Company K and Company R?

    (1) Thee were 17 directors present at joint meeting of the directors of Company K and Company R, and no directors were absent.

    (2) Company K has 12 directors and Company R has 8 directors."

    Another approach is to use the Double Matrix Method. This technique can be used for most questions featuring a population in which each member has two characteristics associated with it.
    Here, we have a population of directors, and the two characteristics are:
    - director at company K or not a director at company K
    - director at company R or not a director at company R

    To learn more about the Double Matrix Method, watch our free video: http://www.gmatprepnow.com/module/gmat-word-problems?id=919

    Once you're familiar with the Double Matrix Method, you can attempt the original question above, as well as these additional practice questions:

    Easy Problem Solving questions
    - http://www.beatthegmat.com/the-aam-aadmi-party-t272242.html
    - http://www.beatthegmat.com/finance-majors-non-finance-majors-overlapping-set-question-t167425.html

    Medium Problem Solving questions
    - http://www.beatthegmat.com/probability-question-t273360.html
    - http://www.beatthegmat.com/posted-speed-limit-t272374.html
    - http://www.beatthegmat.com/motel-t271938.html
    - http://www.beatthegmat.com/of-the-applicants-passes-a-certain-test-15-t270255.html
    - http://www.beatthegmat.com/opening-night-and-late-patrons-t264869.html
    - http://www.beatthegmat.com/ds-french-japanese-t222297.html

    Difficult Problem Solving questions
    - http://www.beatthegmat.com/ratio-problem-t268339.html
    - http://www.beatthegmat.com/overlapping-sets-question-t265223.html
    - http://www.beatthegmat.com/fractions-t264254.html
    - http://www.beatthegmat.com/overlapping-sets-t264092.html
    - http://www.beatthegmat.com/mba/2011/05/09/random-double-matrix-question-2

    Easy Data Sufficiency questions
    - http://www.beatthegmat.com/for-what-percent-of-those-tested-for-a-certain-t270596.html
    - http://www.beatthegmat.com/ds-quest-t187706.html

    Medium Data Sufficiency questions
    - http://www.beatthegmat.com/sets-matrix-ds-t271914.html
    - http://www.beatthegmat.com/each-of-people-voted-once-in-an-election-x-t271375.html
    - http://www.beatthegmat.com/a-manufacturer-t270331.html
    - http://www.beatthegmat.com/in-costume-for-halloween-t269355.html
    - http://www.beatthegmat.com/mba/2011/05/05/random-double-matrix-question-1

    Difficult Data Sufficiency questions
    - http://www.beatthegmat.com/double-set-matrix-question-t271423.html
    - http://www.beatthegmat.com/sets-t269449.html
    - http://www.beatthegmat.com/mba/2011/05/16/random-double-matrix-question-3

    Cheers,
    Brent

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

    Check out the online reviews of our course
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    Last edited by Brent@GMATPrepNow on Thu May 08, 2014 1:08 pm; edited 1 time in total

    Thanked by: vittovangind
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    abhigupta85 Newbie | Next Rank: 10 Posts Default Avatar
    Joined
    08 May 2014
    Posted:
    2 messages
    Post Thu May 08, 2014 10:08 am
    Brent

    Can you please draw double matrix for this question.

    Thanks
    Abhishek

    abhigupta85 Newbie | Next Rank: 10 Posts Default Avatar
    Joined
    08 May 2014
    Posted:
    2 messages
    Post Thu May 08, 2014 10:18 pm
    ttp://postimg.org/image/ui049yr8v/" target="_blank">

    Post Fri May 09, 2014 1:55 am
    abhigupta85 wrote:
    ttp://postimg.org/image/ui049yr8v/" target="_blank">
    Perfect! The tricky part is recognizing that there are zero attendees in the bottom-right box.

    Cheers,
    Brent

    _________________
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    Use our video course along with Beat The GMAT's free 60-Day Study Guide

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    GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!

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