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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 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) = x/12

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) = x+16/18


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


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