# 13.     Two balls are drawn at random with replacement from a box containing black and  red balls. Find the probability that                (iii) one of them is black and other is red.

S seema garhwal

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

Let the first ball is black and the second ball is red.

The probability of getting a black ball in the first draw

The ball is replaced after drawing the first ball.

The probability of getting a red ball in the second draw

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

Let the first ball is red and the second ball is black.

The probability of getting a red ball in the first draw

The probability of getting a black ball in the second  draw

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

Thus,

The probability that one of them is black and the other is red = the probability that the first  ball is black and the second is red  + the probability that the first  ball is red and the second is black

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