Question

A bag contains 12 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.

A 20 Correct Answer Incorrect Answer
B 45 Correct Answer Incorrect Answer
C 36 Correct Answer Incorrect Answer
D 50 Correct Answer Incorrect Answer
E None of these Correct Answer Incorrect Answer

Solution

Number of white balls = 12
Let x be the number of black balls.
Total number of balls in the bag = 12 + x
Also, the probability of drawing a black ball from the bag is thrice that of drawing a white ball.
⇒ x/(12 + x) = 3[12/(12 + x)]
⇒ x = 3 × 12 = 36
Hence, the number of black balls in the bag = 36

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