Question

A bag contain 15 white and some black balls. If the probability of drawing a black ball from the bag is thrice that of drawing a white ball . Find the no of black balls in the bag ?

Answer 1

Answer:

Step-by-step explanation:

No. of white balls=15

let the no. of black balls = x

probability of drawing a white ball = 15/(15+x)

probability of drawing a black ball = x/(15+x)

According to given condition-

x/(15+x)=3*15/(15+x)

x=3*15

=45

therefore the no. of black balls = 45

Answer 2

Let bag contain 'x' black balls.

n(S)=15+x

A=picking a white ball.

n(A)=15/15+x

B=picking a black ball.

n(B)=x/15+x

From given condition,

3n(B)=n(A)

3*x/15+x=15/15+x

x^2+10x-75=0

x=5

So no. of black balls is 5.