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 probablyty of drawing a red ball doubles then what it was before. Find tue number of red balls in the bag.

Answer 1

I think it is the correct answer

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

∴ There are 3 red balls in the bag.