Question

A bag contains 15 white and some black balls if the probability of drawing a black ball from the bag in thrice of drawing a white ball find the number of black balls in the bag

Answer 1

hope u get ....
actually sir I think questions is wrong because. balls can't come in point

Answer 2

Let, No of black balls n(b) = x
No of white balls n(w) = 15
total number of balls= n(b) +n(w) = x+15

P(b) = n(b)/ {n(b) +n(w)}
= x/(x+15)

P(w)= n(w)/{n(b)+n(w)}
= 15/(x+15)
As the question says,
P(b) =3×P(w)
Therefore,
x/(x+15) = 3×15/(x+15)
or, x=45
Hence, The number of Black balls in the bag will be 45.