A bag contains 20 white and some black balls. If the probability of drawing a black ball from the bag is 1.3 times that of drawing a white ball, find the number of black balls in the bag.

Number of white balls = 20

Let x be the number of black balls.

Total number of balls in the bag = 20 + x

Also, the probability of drawing a black ball from the bag is 1.3 times that of drawing a white ball.

⇒ x/(20 + x) = 1.3 [20/(20 + x)]

⇒ x = 1.3 × 20 = 26

Hence, the number of black balls in the bag = 26

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