(11) U
TI
A box contains some black balls and 30 white ha
If the probability of drawing a black ball is two
of a white ball, find the number of black balls in the
box.
[ICSE 2013

More clarification

Step-by-step explanation:

2 of a white ball =2/30 =1/15;

This is the probability of picking a black ball.

Let the number of black ball be X

x/(x +20)= 1/15[ probability of picking black ball ]

15x = x + 20 ; by cross multiplication

14x=20; x = 20/ 14 =1.42 = 1 [ approximately]

But to satisfy the premise given above; we have to approximate the no of balls to 2