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Discussion :: Probability

  1.  A bag contains 2 red, 3 green and 2 blue balls.Two balls are drawn at random.What is the probability that none of the drawn ball is blue?

  2. A.

    5/21

    B.

    10/21

    C.

    15/21

    D.

    20/21

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    Answer : Option B

    Explanation :

    Possible out comes(E) or Favourable outcomes are
    E1.2 red ball or
    E2.2 green ball or
    E3.1 red and 1 green
    Number of selecting 2 balls from two red balls n(E)=2C2=1
    Number of ways of selecting 2 balls from 3 green balls n(E2)=  3C2=3
    Number of ways of selecting 1 red ball and 1 green ball n(E3)= 2C1*3C1=2*3=6
    Sample space S=Number of ways of selecting 2 balls from 7(2+3+2) balls n(S)=7C2=21
    n(E)=n(E1)+ n(E2)+ n(E3)=1+3+6=10
    Required probability P(E)=n(E)/n(S)=10/21


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