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Probability problem...need explanation plzz

This topic has 2 expert replies and 2 member replies
akpareek Senior | Next Rank: 100 Posts Default Avatar
Joined
14 Feb 2010
Posted:
38 messages

Probability problem...need explanation plzz

Post Wed Sep 04, 2013 11:03 am
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    M= {-6, -5, -4, -3, -2}
    T= {-2, -1, 0, 1, 2, 3}

    If an integer is to be randomly selected from set M above and an integer is to be randomly selected from set T above, what is the probability that the product of the two integers will be negative?

    A. 0
    B. 1/3
    C. 2/5
    D. 1/2
    E. 3/5

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    Post Wed Sep 04, 2013 11:12 am
    akpareek wrote:
    M= {-6, -5, -4, -3, -2}
    T= {-2, -1, 0, 1, 2, 3}

    If an integer is to be randomly selected from set M above and an integer is to be randomly selected from set T above, what is the probability that the product of the two integers will be negative?

    A. 0
    B. 1/3
    C. 2/5
    D. 1/2
    E. 3/5
    IMPORTANT: the number chosen from set M is ALWAYS negative.
    So, the only way to get a negative product is when the number chosen from set T is POSITIVE.

    P(number chosen from set T is positive) = 3/6 = 1/2 = D

    Cheers,
    Brent

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    vipulgoyal Master | Next Rank: 500 Posts Default Avatar
    Joined
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    Posted:
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    Post Wed Sep 04, 2013 8:39 pm
    no is positive = [1 - no is negtive + no is O]
    [1- (5/5*2/6 + 5/5*1/6]
    1-1/2=1/2

    madhusudhan237 Newbie | Next Rank: 10 Posts Default Avatar
    Joined
    30 Oct 2015
    Posted:
    5 messages
    Post Thu Dec 24, 2015 7:23 am
    Brent@GMATPrepNow wrote:
    akpareek wrote:
    M= {-6, -5, -4, -3, -2}
    T= {-2, -1, 0, 1, 2, 3}

    If an integer is to be randomly selected from set M above and an integer is to be randomly selected from set T above, what is the probability that the product of the two integers will be negative?

    A. 0
    B. 1/3
    C. 2/5
    D. 1/2
    E. 3/5
    IMPORTANT: the number chosen from set M is ALWAYS negative.
    So, the only way to get a negative product is when the number chosen from set T is POSITIVE.

    P(number chosen from set T is positive) = 3/6 = 1/2 = D

    Cheers,
    Brent
    HI Brent

    Cannot i solve this problem the following way?

    P(that product of 2 integers is -ve) = 1 - P(that product of 2 integers is +ve)
    = 1 - [ P(integer selected from set"M" is -ve) AND P(integer selected from set T is -ve)]
    = 1 - [ (5/5) * (2/6)]
    = 1 - (1/3)
    = 2/3

    Where am i getting this wrong?

    Post Thu Dec 24, 2015 9:13 am
    Hi madhusudhan237,

    Set T contains a 0, so you ALSO have to factor in the possibility that the product of the two numbers will be 0 (and subtract that outcome as well). Your solution did not include that possibility.

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