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

Total number of black balls = x

Total number of balls = 12

Total number of outcomes = 12

p(x)= x/12

When 6 more black balls are put in the box, total number of balls = 12 + 6 = 18 then

Number of black balls = 6 + x

p(black)= x+6/18

as per condition

x+6/18= 2*x/12

x+6= 3x

x=3

Answer

Number of black balls = 3

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