Q. 225.0( 13 Votes )
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.
Given: Total balls = 12
Black balls = x
Probability of drawing a black ball, P(black)
Now 6 black balls are added to the box, therefore,
Total balls = 12 + 6 = 18
Black balls = x + 6
Let the new probability be P(new)
P(new) = 2.P(black)
Cross multiplying, we get,6x + 36 = 18x
18x - 6x = 36
12x = 36
x = 3
Hence, value of x is 3.
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