Question

A bag contains 5 red balls and some blue balls. If the probability of drawing a blue ball is double that of a red ball, determine the number of blue balls in the bag.

Answer 1

Let the number of blue balls in the bag be x.

Then total number of balls = (5 + x)

∴ Total number of possible outcomes = (5 + x)

∴ P(a blue ball) = x/(5+x)

∴ P(a red ball) = 5/5+x

According to question P (a blue ball) = 2 × P(a red ball)

⇒ x = 10.

Hence, number of blue balls in the bag = 10.