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) = 18x
6x + 36 = 18x
36 = 18x - 6x
36 = 12x
3 = x