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-

Answer: Option C

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
∴ $$\frac{40x+384}{x+12}$$  = 36
⇒ 40x + 384 = 36x + 432
⇒ 4x = 48
⇒ x = 12
Hence, the original strength of the class = 12