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03/07/2021 10:49 am
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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 is now double of what it was before. Find x
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03/07/2021 10:51 am
Total number of black balls = x
Total number of balls = 12
P(E) = (Number of favourable outcomes/ Total number of outcomes)
P (getting black balls) = x/12 .........(i)
Now, when 6 more black balls are added,
Total balls become = 18
∴ Total number of black balls = x+6
Now, P (getting black balls) = (x+6)/18 ...........(ii)
It’s given that, the probability of drawing a black ball now is double of what it was before
(ii) 2 × (i)
(x + 6)/18 = 2 × (x/12)
x + 6 = 3x
2x = 6
∴ x = 3