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

Melting cube!

This topic has 1 expert reply and 0 member replies
vinay1983 GMAT Destroyer!
Joined
14 Aug 2013
Posted:
643 messages
Followed by:
6 members
Thanked:
48 times
Target GMAT Score:
650+
Melting cube! Post Mon Sep 30, 2013 6:54 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    A large cube is formed from the material obtained by melting 3 cubes of sides 3 units, 4 units and 5 units. What is the ration of the sum of the total surface area of the small cubes to that of the large cubes?

    A. 1:1
    B. 12:7
    C. 25:18
    D. 12:13
    E. 12:17

    _________________
    You can, for example never foretell what any one man will do, but you can say with precision what an average number will be up to!

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    Post Mon Sep 30, 2013 7:07 am
    vinay1983 wrote:
    A large cube is formed from the material obtained by melting 3 cubes of sides 3 units, 4 units and 5 units. What is the ration of the sum of the total surface area of the small cubes to that of the large cube?

    A. 1:1
    B. 12:7
    C. 25:18
    D. 12:13
    E. 12:17
    Total volume of all 3 cubes
    (3x3x3) + (4x4x4) + (5x5x5) = 27 + 64 + 125 = 216
    So, the NEW cube must have volume of 216 cubic units
    If we let k be length of one side of NEW cube, then we know that k^3 = 216
    Solve, to get k = 6
    So, the NEW cube has dimensions 6x6x6

    Total surface of the 3 original cubes
    6(3x3) + 6(4x4) + 6(5x5) = 6(9) + 6(16) + 6(25)
    = 6(50)

    Total surface of the NEW cube
    6(6x6) = 6(36)

    The ratio of total surface area of the small cubes to that of the NEW cube = 6(50)/6(36)
    = 50/36
    = 25/18
    = C

    Cheers,
    Brent

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

    Thanked by: irfanali
    GMAT Prep Now's 35-hour (500+ videos) course is 100% FREE. Use our free course in conjunction with Beat The GMAT’s FREE 60-Day Study Guide and reach your target score in 2 months!

    Best Conversation Starters

    1 NandishSS 28 topics
    2 fiza gupta 20 topics
    3 Mo2men 11 topics
    4 Anaira Mitch 10 topics
    5 gabrielrc 7 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    109 posts
    2 image description GMATGuruNY

    The Princeton Review Teacher

    91 posts
    3 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    79 posts
    4 image description DavidG@VeritasPrep

    Veritas Prep

    70 posts
    5 image description Jay@ManhattanReview

    Manhattan Review

    63 posts
    See More Top Beat The GMAT Experts