• Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider

Bert and Clair's coins (OG13)

This topic has 2 expert replies and 2 member replies
alex.gellatly Master | Next Rank: 500 Posts Default Avatar
Joined
16 Nov 2011
Posted:
435 messages
Followed by:
16 members
Thanked:
48 times

Bert and Clair's coins (OG13)

Post Thu Aug 02, 2012 10:02 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    What is the total number of coins that Bert and Claire have?
    (1) Bert has 50 percent more coins than Claire.
    (2) The total number of coins that Bert and Claire have is between 21 and 28.

    OK, I got the correct answer by picking numbers and kind of guessing. Can someone show me a good algebraic approach?

    Thanks!

    _________________
    A useful website I found that has every quant OG video explanation:

    http://www.beatthegmat.com/useful-website-with-og-video-explanations-t112985.html#475231

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!

    GMAT/MBA Expert

    Anurag@Gurome GMAT Instructor
    Joined
    02 Apr 2010
    Posted:
    3835 messages
    Followed by:
    518 members
    Thanked:
    1852 times
    GMAT Score:
    770
    Post Thu Aug 02, 2012 10:12 pm
    alex.gellatly wrote:
    What is the total number of coins that Bert and Claire have?
    (1) Bert has 50 percent more coins than Claire.
    (2) The total number of coins that Bert and Claire have is between 21 and 28.

    OK, I got the correct answer by picking numbers and kind of guessing. Can someone show me a good algebraic approach?

    Thanks!
    Let us assume that the no. of coins that Bert has = B, and
    no. of coins that Claire has = C
    We have to find the value of B + C.

    (1) Bert has 50% more coins than Claire implies B = C + 0.50C or B = 1.5C
    So, B + C = 1.5C + C = 2.5C, but we do not know the value of C; NOT sufficient.

    (2) The total number of coins that Bert and Claire have is between 21 and 28 implies 21 < (B + C) < 28.
    This means B + C can be 22, 23, 24, 25, 26, or 27. But there is no unique value; NOT sufficient.

    Combining (1) and (2), B + C = 2.5C and 21 < (B + C) < 28
    21 < 2.5C < 28
    21/2.5 < C < 28/2.5
    8.4 < C < 11.2 implies C can be 9 or 10.

    When C = 9, B = 1.5C = 1.5 * 9 = 13.5, which is not possible as B is the no. of coins that Bert has, which should be an integer.
    When C = 10, B = 1.5C = 1.5 * 10 = 15. Here B + C = 15 + 10 = 25; SUFFICIENT.

    The correct answer is C.

    _________________
    Anurag Mairal, Ph.D., MBA
    GMAT Expert, Admissions and Career Guidance
    Gurome, Inc.
    1-800-566-4043 (USA)

    Join Our Facebook Groups
    GMAT with Gurome
    https://www.facebook.com/groups/272466352793633/
    Admissions with Gurome
    https://www.facebook.com/groups/461459690536574/
    Career Advising with Gurome
    https://www.facebook.com/groups/360435787349781/

    Post Fri Aug 03, 2012 9:02 am
    I> Not Sufficient because total coins are
    x+1.5x=2.5x (X can take any value)
    II> Not Sufficient because total coins could be anything between
    21 to 28
    Taking
    I+II> 2.5x will be between 21 and 28
    25 could be 1 value
    Lets search for other values(should be less than or more than in multiples of 2.5)
    25-2.5*(1) = 22.5 (Not possible)
    25-2.5*(2) = 20 (Less than 21)
    Similarly,
    25+2.5*(1) = 27.5 (Not possible)
    25+2.5*(2) = 30 (More than 28)

    Hence answer is C.

    Post Fri Aug 03, 2012 10:09 am
    alex.gellatly wrote:
    What is the total number of coins that Bert and Claire have?
    (1) Bert has 50 percent more coins than Claire.
    (2) The total number of coins that Bert and Claire have is between 21 and 28.

    OK, I got the correct answer by picking numbers and kind of guessing. Can someone show me a good algebraic approach?

    Thanks!
    This problem is restricted to POSITIVE INTEGERS.

    Statement 1: Bert has 50 percent more coins than Claire.
    Thus, if C=2, then B = (1.5)2 = 3, implying that B:C = 3:2.
    Since the sum of the parts of this ratio = 3+2 = 5, the total number of coins must be a multiple of 5.
    INSUFFICIENT.

    Statement 2: The total number of coins that Bert and Claire have is between 21 and 28.
    Thus, the total number of coins could be any integer between 21 and 28.
    INSUFFICIENT.

    Statements 1 and 2 combined:
    The only multiple of 5 between 21 and 28 is 25.
    SUFFICIENT.

    The correct answer is C.

    _________________
    Mitch Hunt
    GMAT Private Tutor
    GMATGuruNY@gmail.com
    If you find one of my posts helpful, please take a moment to click on the "Thank" icon.
    Available for tutoring in NYC and long-distance.
    For more information, please email me at GMATGuruNY@gmail.com.

    Free GMAT Practice Test How can you improve your test score if you don't know your baseline score? Take a free online practice exam. Get started on achieving your dream score today! Sign up now.
    vinodsundaram Senior | Next Rank: 100 Posts Default Avatar
    Joined
    21 May 2012
    Posted:
    58 messages
    Thanked:
    1 times
    Test Date:
    08/16/2012
    Target GMAT Score:
    720
    Post Mon Aug 06, 2012 1:36 am
    there's catch in these kind of problems.

    Once you combine both equations, you solve and get multiple answers.
    It is important to ELIMINATE All possible wrong answers.

    We know Coins can always be Positive numbers. Hence using the relation between B and C we can eliminate.

    Best Conversation Starters

    1 Vincen 203 topics
    2 Roland2rule 65 topics
    3 lheiannie07 57 topics
    4 ardz24 44 topics
    5 lionsshare 14 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    157 posts
    2 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    103 posts
    3 image description GMATGuruNY

    The Princeton Review Teacher

    98 posts
    4 image description Jay@ManhattanReview

    Manhattan Review

    95 posts
    5 image description Matt@VeritasPrep

    Veritas Prep

    80 posts
    See More Top Beat The GMAT Experts