In a school with 600 students, the average age of the boys is 12 years and that of the girls is 11 years. If the average of the school is 11 years 9 months, then the average the number of girls in the school is :

A. 150

B. 250

C. 350

D. 450

Answer: Option A

Solution(By Examveda Team)

Let the number of girls be x
Then, number of boys = (600 - x)
Then,
$$\left( {11\frac{3}{4} \times 600} \right)$$   = 11x + 12 (600 - x)
⇔ x = 7200 - 7050
⇔ x = 150