Question

In a school with 1200 students, the average age of the boys is 12 years and the average age of girls is 11 years. If the average age of the school is 11 years 6 months, then the number of girls in the school is:
1. 600
2. 550
3. 500
4. 750
5. 700

Answer 1

Correct Answer - Option 1 : 600

Given:

Total students = 1200

Average of Boys & Girls = 12 & 11 years respectively.

Average of class = 11 years 6 months

Assumption:

Let the number of girls be x

The number of boys = (1200 - x)

Calculation:

 According to the question:

⇒ 11 ½ × 1200 = 11x + 12(1200 - x)

⇒ 13800 = 11x + 14400 – 12x

⇒ x = 600

∴The total number of girls in the class is 600.