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 Apex Team)

Let the number of girls be x Then, number of boys = (600 – x) Then, $\begin{array}{l}\left(11\frac{3}{4}\times600\right)=11x+12(600-x)\\ \Leftrightarrow x=7200-7050\\ \Leftrightarrow x=150\end{array}$

A. 20
B. 21
C. 28
D. 32

A. 18
B. 20
C. 24
D. 30

A. 10 years
B. 10.5 years
C. 11 years
D. 12 years