Question

A box contain some black balls and 30 white balls. If the probability of drawing a white ball is one third, find the number of black balls in the box.

Answer 1

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Answer 2

Answer:

90

Step-by-step explanation:

Let the number of Black Balls in the box = x

Number of White Balls in the box = 30

Total Balls = x + 30

Now Probability of drawing a White Ball = 30/(30+x)

Probability of drawing a Black Ball = x/(x+30)

According to Question

P(White Ball) = 1/3 P(White Ball)

$\frac{30}{x+30}=\frac{1}{3} \times \frac{x}{x+30}$

x = 90

∴ Number of Black Balls in the Box is 90