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.

Answer :

Given: Total balls = 12


Black balls = x


Concept Used:



Explanation:


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)


Now,


P(new) = 2.P(black)


Therefore,



Cross multiplying, we get,

6x + 36 = 18x

18x - 6x = 36

12x = 36

x = 3

Hence, value of x is 3.

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