# 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

**Solution:**

We use the basic formula of probability to find the number of blue balls.

First, find out the total number of outcomes and all the possible outcomes. Now, to find the probability use the formula given below

Probability = No. of possible outcomes / Total no. of outcomes

As it is given in the question that the probability of drawing a blue ball is double that of a red ball, that means

2 × probability of drawing red ball = probability of drawing the blue ball.

Put the values in the above and you can find out the number of blue balls.

No. of red balls = 5

Let the no. of blue balls be x

Total number of balls = x + 5

Probability of drawing red ball = No. of possible outcomes / Total no. of outcomes

= 5/(x + 5)

Probability of drawing blue ball = No. of possible outcomes / Total no. of outcomes

= x/(x + 5)

Since the probability of drawing a blue ball is double that of a red ball

x/(x + 5) = 2 [5/(x + 5)]

x = 10

Hence the number of blue balls = 10

Check out more about the terms of probability.

**Video Solution:**

## 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

### NCERT Solutions for Class 10 Maths - Chapter 15 Exercise 15.2 Question 3:

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

If a bag contains 5 red balls and some blue balls, the probability of drawing a blue ball is double that of a red ball, then the number of blue balls in the bag is 10.