A box contains 4 white and 5 black balls. A ball is drawn at random and its colour is noted. A ball is then put back in the box along with two additional balls of its opposite colour. If a ball is drawn again from the box, then the probability that the ball drawn now is black, is

A box contains 4 white and 5 black balls. A ball is drawn at random and its colour is noted. A ball is then put back in the box along with two additional balls of its opposite colour. If a ball is drawn again from the box, then the probability that the ball drawn now is black, is

  1. A

    711

  2. B

    511

  3. C

    5399

  4. D

    4899

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    Solution:

    Consider the following events:

        E1 : Ball drawn from the box is white

        E2 : Ball drawn from the box is black

       A =Getting a black ball from the box after replacing the drawn ball with two balls of opposite colour

      PE1=49,PE2=59,PA/E1=711,PA/E2=511

     P(A)=PE1PA/E1+PE2PA/E2=49×711+59×511=5399

     

     

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