Question
A bag contains 25 white and some black balls. If
the probability of drawing a black ball from the bag is thrice that of drawing a white ball, find the number of black balls in the bag.Solution
Number of white balls = 25
Let x be the number of black balls.
Total number of balls in the bag = 25 + x
Also, the probability of drawing a black ball from the bag is thrice that of drawing a white ball.
⇒ x/(25 + x) = 3 [25/(25 + x)]
⇒ x = 3 × 25 = 75
Hence, the number of black balls in the bag = 75
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