Question

A box contains 24 balls of which some are yellow in colour. If 12 more yellow balls are put in the box and a ball is drawn at random, the probability of drawing a yellow ball doubles what what was it before.find the number of yellow balls in the bag

Answer 1

Let the no. of yellow balls be x.
P(yellow ball)=x/24

Now,12 more yellow balls are put in the box.
Total no. of balls=24+12=36
No. of yellow balls=x+12
P(yellow balls after adding 12 yellow balls)=(x+12)/36

2 times of P(yellow ball)=P(yellow balls after adding 12 yellow balls)
2*x/24=(x+12)/36
x/12=(x+12)/36
36*x=12*(x+12)
36x=12x+144
36x-12x=144
24x=144
x=144/24
x=6
There are 6 yellow balls in the box