• 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
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas 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
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

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

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • 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
  • 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
  • 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

What is the probability that events A and B both occur?

This topic has 5 member replies
sanjib Master | Next Rank: 500 Posts Default Avatar
Joined
10 May 2009
Posted:
109 messages

What is the probability that events A and B both occur?

Post Fri Sep 04, 2009 8:11 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    What is the probability that events A and B both occur?
    (1) The probability that event A occurs is 0.8.
    (2) The probability that event B occurs is 0.6.
    I think the answer is 1-(both do not occur) so in order to get both do not occur we need both st.1 and st.2.Therefore it should be C.
    But its not the OA. Am I missing something.

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    aakaps Junior | Next Rank: 30 Posts Default Avatar
    Joined
    07 Jul 2009
    Posted:
    27 messages
    Thanked:
    1 times
    Target GMAT Score:
    780
    GMAT Score:
    740
    Post Sat Sep 05, 2009 6:53 pm
    good question!! I just came back from my usual starbucks joint where I solve my practise problems and faced exactly same question.

    So the answer is.....1-both dont occur means....both will NOT occur, together or seperate. Whereas the question is both to occur together.

    So the answer has to be probability of first to occur and then probability of second to occur. Both will multiply. Also you need to check whether the sequence matters. If yes, then multiply by 2, else you have your answer.

    bharathh Master | Next Rank: 500 Posts Default Avatar
    Joined
    27 Aug 2009
    Posted:
    159 messages
    Thanked:
    19 times
    Post Sat Sep 05, 2009 6:58 pm
    I would have gone for C as well.

    I'm guessing it's E because you don't know if A and B are mutually exclusive events... ie. If A occurs B will not occur and vice versa.

    If they are not mutually exclusive, it is not possible to calculate probability.

    sanjib Master | Next Rank: 500 Posts Default Avatar
    Joined
    10 May 2009
    Posted:
    109 messages
    Post Sat Sep 05, 2009 10:24 pm
    Please need more explanation.Because the OA is E.

    qwe12 Senior | Next Rank: 100 Posts Default Avatar
    Joined
    30 May 2009
    Posted:
    60 messages
    Thanked:
    2 times
    Post Sun Sep 06, 2009 1:27 am
    sanjib wrote:
    What is the probability that events A and B both occur?
    (1) The probability that event A occurs is 0.8.
    (2) The probability that event B occurs is 0.6.
    there are 3 formulas joint probability
    http://en.wikipedia.org/wiki/Probability

    p(a or b) = p(a) + p(b) - p(a and b)

    we do not get p(a and b) from (1), (2) or (1) and (2)

    answer (E)

    Nermal Senior | Next Rank: 100 Posts Default Avatar
    Joined
    21 Jun 2009
    Posted:
    77 messages
    Thanked:
    7 times
    Post Sun Sep 06, 2009 1:44 am
    You can only calculate the probability if you know that the occurence of one event is independent from the occurence of the other event.

    Then you could use formula P(A and B) = P(A)*P(B), it would be 0,8*0,6=0,48 (C)

    But since this fact is not explicitly stated we cannot assume any indepence of the occurence of those events, therefore we don't know:
    Answer E

    Best Conversation Starters

    1 LUANDATO 157 topics
    2 lheiannie07 87 topics
    3 Roland2rule 75 topics
    4 ardz24 64 topics
    5 AAPL 58 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description EconomistGMATTutor

    The Economist GMAT Tutor

    163 posts
    2 image description GMATGuruNY

    The Princeton Review Teacher

    133 posts
    3 image description Jay@ManhattanReview

    Manhattan Review

    128 posts
    4 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    121 posts
    5 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    100 posts
    See More Top Beat The GMAT Experts