Q.13.     Two balls are drawn at random with replacement from a box containing 10 black and 8 red balls. Find the probability that

                 (ii)  first  ball is black and second is red.

Answers (1)

Two balls are drawn at random with replacement from a box containing 10 black and 8 red balls.

Total balls =18

Black balls = 10

Red balls = 8

The probability of getting a black ball in the first draw 

                                                                            =\frac{10}{18}=\frac{5}{9}

The ball is replaced after drawing the first ball.

The probability of getting a red ball in the second draw 

                                                                            =\frac{8}{18}=\frac{4}{9}

the probability that the first  ball is black and the second is red

                                                                                     =\frac{5}{9}\times \frac{4}{9}=\frac{20}{81}

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