Question

the solution of this question

Answer 1

let no. of black balls be X
so total no. of balls = 30+X
probability to get a black ball = X/30+X
and probability to get a white ball = 30/30+X
ACC. to qué
X/(30+X)=2*30/5*(30+X)
so X=12
is Ur required result in attachment

Answer 2

No. Of black balls=x Tot no of balls = 30+x. Probability of getting a white ball =30/x+30. Probability of getting a black ball=2/5into30/x+30. Sum of both probability =1. Equate them you'll get it DSTG