Answers

  • qais
  • Content Quality
2015-12-01T11:36:51+05:30
Let number of black ball be x
now total ball will be (30 + x)
probability of getting black ball, P(B) = x/(30+x)
and , probability of getting white ball , P(W) = 30/(30+x)
now, A/Q,
x/(30+x) =2/5 ×(30/(30+x)
⇒x = 12
so, number of black ball is 12
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