Question

a box contains 12 balls out of which X are black if one ball is drawn at random from the box what will be the probability that it will be a black balls if 6 more black balls are put in the box the probability of drawing a black ball is in our double of what it was before find x

Answer 1

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

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Answer 2

Total no. of balls=12

Total black balls=x

P(the ball drawn is black) =x/12

Now when 6 balls are added to the box the total no. of balls are 12+6=18

Now,

New P(drawing black ball) =2[P(drawing black ball)]

Total black balls=x+6

x+6/18=x/12

2x+12=3x

x=12