Question

A box contains 12 balls of which some are red in colour if 6 more red balls are put in the box and a ball is drawn at random, the probability of drawing a red ball doubles than what it was before. Find the number of red balls in the box.

Answer 1

let the no. of red balls be x
now 6 more red balls are in the box
so total no of balls =18
no of red balls are 6+x
so acc to qus
new probability=2 (before probability)
(6+x/18)=(x/12)2
(6+x)/18=x/6
6(6+x)=18x
36+6x=18x
36=12x
x=3
so total no of red balls be (6+3)
=9
hope it will help you

Answer 2

Let number of red balls be = x

P(red ball) = x/12

If 6 more red balls are added:

The number of red balls = x + 6

P(red ball) = (x+6)/18

Since, (x+6)/18 = 2(x/12)

x = 3

Therefore, there are 3 red balls in the bag.