Question

A bag contains 4 red, 5 white and some yellow balls. If probability of drawing a red ball at random is `1/5` then find the probability of drawing a yellow ball at random.

Answer 1

Given that,

Bag contains

Number of red balls = 4

Number of white balls = 5

Let the number of yellow balls be y 

Also, P(red ball) = `1/5`

Total number of balls = 4 + 5 + y = (9 + y)

So, P(red) = `4/((9 + y)) = 1/5`

⇒ `1/5 = 4/((9 + y))`

⇒ (9 + y) = 20

⇒ y = 20 − 9

⇒ y = 11

So, the number of yellow balls is 11.