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 now is double of what it was before. Find x.

number of black balls = *x*

∴ number of favorable outcomes = *x*

total number of balls = 12

∴ total number of outcomes = 12

∴ P (black ball) =

now 6 new black balls added

∴ number of black balls = *x* + 6

∴ number of favorable outcomes = *x + 6*

total number of balls = 12 + 6 = 18

∴ P (black ball) =

according to the question

=

=

6 (*x* + 6) = 18*x*

6*x* + 36 = 18*x*

36 = 18*x *- 6*x*

36 = 12*x*

3 = *x*

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