A box contain some black balls and 30 white balls .If the probability of drawing a
black ball is two - fifth of a white ball. Find the number of black balls in the box.
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Step-by-step explanation:
No. of white balls = 30
No. of black balls = x (say)
Total no. of balls = 30+x
Given : Probability of drawing a black ball, i.e.,
P(B) = 2/5 of P(W).
= x /30+x = 2/5 of 30/30+x
= x/30+x = 12/30+x
= x = 12
Hence, the no. of black balls = 12.
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