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Question
A bag contains 15 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
Suppose number of black ball = x
It is given that White balls = 15
According to question,
P(Black balls) = 3 × P(White balls)
`=> x/(15+x) = 3 xx 15/(15 + x)`
`=> x = 45`
Hence, number of black ball are 45.
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