Welcome! Check out our free B-School Guides to learn how you compare with other applicants.
Login or Register

Triangles in a heptagon

This topic has 1 expert reply and 1 member reply
rahulvsd Really wants to Beat The GMAT! Default Avatar
Joined
07 Sep 2010
Posted:
184 messages
Followed by:
1 members
Thanked:
6 times
Triangles in a heptagon Post Mon Mar 05, 2012 6:46 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    How many triangles can be inscribed in the heptagon pictured, where the three vertices of the triangle are also vertices of the heptagon?



    A.9 B. 21 C. 35 D. 140 E. 210.

    Ans: C. Grockit solves this by using combinations method and I agree with this solution. If the question mentions non-overlapping triangle, will the answer be 5. By using formula (n-2) *180, so here it will be 5 * 180 so 5 triangles, is this approach correct? And if the question was rephrased as number of triangles (does not mention non - overlapping) in a hexagon by the combination method answer will be 6 factorial / 3 factorial * 3 factorial. So 20 triangles, is this correct too? please confirm...

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    pemdas GMAT Titan Default Avatar
    Joined
    15 Apr 2011
    Posted:
    1085 messages
    Followed by:
    21 members
    Thanked:
    156 times
    Post Mon Mar 05, 2012 10:58 am
    i selected this option --> one vertice needs two more vertices to form triangle and in total three vertices will be required out of seven, 7C3=35

    c

    _________________
    Success doesn't come overnight!

    GMAT/MBA Expert

    Post Mon Mar 05, 2012 11:14 am
    35 is the answer: 7*6*5/3!

    _________________
    GMAT Answers provides a world class adaptive learning platform.
    -- Push button course navigation to simplify planning
    -- Daily assignments to fit your exam timeline
    -- Organized review that is tailored based on your abiility
    -- 1,000s of unique GMAT questions
    -- 100s of handwritten 'digital flip books' for OG questions
    -- 100% Free Trial and less than $20 per month after.
    -- Free GMAT Quantitative Review

    Best Conversation Starters

    1 rommysingh 47 topics
    2 yass20015 30 topics
    3 tapanmittal 13 topics
    4 rakaisraka 12 topics
    5 j_shreyans 12 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    155 posts
    2 image description GMATGuruNY

    The Princeton Review Teacher

    153 posts
    3 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    132 posts
    4 image description DavidG@VeritasPrep

    Veritas Prep

    67 posts
    5 image description Max@Math Revolution

    Math Revolution

    63 posts
    See More Top Beat The GMAT Experts