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A box contains 12 balls out of which x are black . If one ball is drawn at random from the box, what is the probability that it will be a black ball? If 6 more black balls are put in the box, the probability of drawing a black ball is now double of what it was before. Find the value of x.

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answer is A.

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Detailed Solution

Initially, total number of balls = 12
Number of black balls = x
So, P (black ball) =

\frac{x}{12}

If 6 more black balls are added, total number of balls = 12+ 6 =18
Number of black balls = x+6

Given the probability of drawing a black ball is now double of what it was before
So,
Question Image

So, the number of black balls present initially is 3.
Hence, Option (1) is the correct answer.

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