The average age of an adult class is 40 years. 12 new students with an average age of 32 years join the class, thereby decreasing the average by 4 years. The original strength of the class was-

A. 10 B. 11 C. 12 D. 15 Answer: Option C

Solution(By Apex Team)

Let the original strength of the class be x Sum of ages of the whole class = 40x years Sum of ages of 12 now students = (12 × 32) years = 384 years \begin{aligned}\frac{40x+384}{x+12}=36\\ \end{aligned} $\begin{array}{l} \Rightarrow 40 x+384=36 x+432 \\ \Rightarrow 4 x=48 \\ \Rightarrow x=12 \end{array}$ Hence, the original strength of the class = 12

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