A bag has red and blue balls in the ratio 4 : 5. If the total number of balls is 81, then find the number of blue balls.

Correct option is B

Given:

The ratio of red to blue balls = 4:5

Total number of balls = 81

Concept Used:

If the ratio of two quantities is a:b, then their actual values can be found using the formula:

Total=a+ b

​$$\text{Each part} = \frac{\text{Total}}{\text{Sum of ratio terms}} \times \text{Respective ratio term}$$​​

Solution:

Total parts in the ratio:

4+5=9

Each part value:

​$$\frac{81}{9} = 9$$​​

Number of blue balls:

5×9=45

Option (B) is right.