Question

A bag contains 8 red and some blue balls. One ball is drawn at random from the bag. If ratio of probability of getting red ball and blue ball is 2:5, then find the number of blue balls.

Answer 1

We are given:

• Number of red balls = 8

• Let the number of blue balls = x

• Total balls = 8 + x

• The ratio of probabilities of getting a red ball to a blue ball is 2:5

Step 1: Write probabilities

Probability of red ball = `8/(8+x)`

Probability of blue ball = `x/(8+x)`

Given:

`(P(Red))/(P(Blue)) = 8/(8+x) div x/(8+x) = 8/x = 2/5`

`8/x = 2/5`

8 × 5 = 2 × x ⇒ 40 = 2x

`x = 40/2`

= 20