Question

In a class there are only 25% girls. If average age of the girls in the class is 8 years and average age of whole class is 12 ½ years. Find the average age of boys in the class.
1. 1
2. 2
3. 3
4. None of these

Answer 1

Correct Answer - Option 4 : None of these

Given:

Total number of girls in the class = 25% of total students

Total number of boys = 100% - 25% = 75% of total students

Average age of girls = 8 years

Average age of total students = 12 ½ years

Formula used:

Average = Total sum / Total number

Total sum = Average × Total number

Ratio between the number of boys and number of girls = 75 ∶ 25 = 3 ∶ 1

Let, number of boys = 3x, number of girls = x and total students = 4x

∵ Average age of girls = 8 years

∴ Total age of the girls = 8 × x = 8x

And, average age of whole class = 12 ½ years

∴ Total age of all the students = 25/2 × 4x = 50x

∴ Total age of all boys = 50x – 8x = 42x

∴ Average age of boys = 42x/3x = 14

Therefore, average age of boys in the class = 14 years