#### Question

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 *x*.

#### Solution

Total number of balls = 12

Total number of black balls = *x*

P (getting a black ball) = x/12

If 6 more black balls are put in the box, then

Total number of balls = 12 + 6 = 18

Total number of black balls = *x* + 6

P (getting a black ball now) = (x+6)/18

According to the condition given in the question,

`2(x/12) - (x+6)/18`

3x = x+6

2x = 6

x = 3

Is there an error in this question or solution?

Solution 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? Concept: Probability - A Theoretical Approach.