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

Probability (Marbles in a bag)

This topic has 1 expert reply and 0 member replies
Bookmark
Previous Topic Next Topic
ashfu2002 Just gettin' started! Default Avatar
Joined
19 Mar 2012
Posted:
4 messages
Probability (Marbles in a bag) Post Tue Apr 03, 2012 10:22 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    A bag contains some red and some blue marbles.How many red marbles are in the bag?

    (1) If two marbles are selected from the bag, the probability of selecting one red and one blue marble is 1/4

    (2) There are a total of 8 marbles in the bag.

    OA E

    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

    Bill@VeritasPrep GMAT Instructor
    Joined
    29 Mar 2012
    Posted:
    1002 messages
    Followed by:
    138 members
    Thanked:
    389 times
    Target GMAT Score:
    800
    GMAT Score:
    780
    Post Tue Apr 03, 2012 10:48 am
    1) There are two ways of getting one blue and one red, each of which has the same probability:

    B-R
    R-B

    Since the total probability is 1/4, P(B-R)=1/8 and P(R-B)=1/8. If we have 7 red and 1 blue, then P(R-B) = 7/8 * 1/7 = 7/56 = 1/8. P(B-R) would have the same probability for a total of 1/4. However, we can also arrive at the same probability if we have 7 blue and 1 red. Insufficient.

    2) R + B = 8. There are many possible combinations of red and blue marbles. 1 and 7, 2 and 6, and so on. Insufficient.

    When put together, we still have the same possibilities we had in Statement 1, so we still cannot answer.

    _________________
    Take your GMAT prep on the go!

    For the first time, you can complete a full GMAT prep course on your mobile device. Download each of Veritas Prep’s 12 GMAT lessons directly on your iPad and iPhone.

    Download the Veritas Prep GMAT On Demand App Free

    Access The Veritas Prep GMAT Simulator™- for FREE! Veritas Prep has launched their new GMAT Practice Test. Sign up to access the realistic testing environment and challenge yourself today! Get Started Now.

    Best Conversation Starters
    1 varun289 40 topics
    2 guerrero 21 topics
    3 sana.noor 20 topics
    4 killerdrummer 19 topics
    5 sanaa.rizwan 14 topics
    See More Top Beat The GMAT Members...

    Most Active Experts
    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    		 203 posts
    2 image description GMATGuruNY

    The Princeton Review Teacher

    		 140 posts
    3 image description Jim@StratusPrep

    Stratus Prep

    		 100 posts
    4 image description Anju@Gurome

    Gurome

    		 99 posts
    5 image description Jon@Admissionado

    Admissionado

    		 49 posts
    See More Top Beat The GMAT Experts