Question
A bag contains 19 white and some black balls. If
the probability of drawing a black ball from the bag is twice that of drawing a white ball, find the number of black balls in the bag.Solution
Number of white balls = 19
Let x be the number of black balls.
Total number of balls in the bag = 19 + x
Also, the probability of drawing a black ball from the bag is twice that of drawing a white ball.
⇒ x/(19 + x) = 2[19/(19 + x)]
⇒ x = 2 × 19 = 38
Hence, the number of black balls in the bag = 38
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