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:
    1086 messages
    Followed by:
    21 members
    Thanked:
    155 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

    Jim@StratusPrep MBA Admissions Consultant
    Joined
    11 Nov 2011
    Posted:
    2028 messages
    Followed by:
    239 members
    Thanked:
    600 times
    GMAT Score:
    770
    Post Mon Mar 05, 2012 11:14 am
    35 is the answer: 7*6*5/3!

    _________________
    If you find my posts helpful. Please take the time to click the "thank" icon at the top of the page and/or follow me!

    For in-person tutoring and help visit Stratus Prep:

    GMAT Tutoring | MBA Admission Consulting | GMAT Diagnostic Exam


    For my personally written study guides and online courses visit GMAT Prepster:
    GMAT Quant Diagnostic | Online GMAT Courses | GMAT Prep

    Best Conversation Starters

    1 melanie.espeland 28 topics
    2 aditya8062 18 topics
    3 Rastis 14 topics
    4 chacha0212 13 topics
    5 yadu9991 12 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description GMATGuruNY

    The Princeton Review Teacher

    104 posts
    2 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    82 posts
    3 image description CriticalSquareMBA

    Critical Square

    55 posts
    4 image description MBAPrepAdvantage

    MBAPrepAdvantage

    24 posts
    5 image description Jon@Admissionado

    Admissionado

    20 posts
    See More Top Beat The GMAT Experts