The average age of A, B and C is 20 years, and that of B and C is 25 years. What is the age of A?

Given, the average age of A, B and C is 20 years

$$\Rightarrow$$  Sum of the ages of A, B and C = 20 x 3 = 60 years

$$\Rightarrow$$  A + B + C = 60 ..........(1)

Average age of B and C is 25 years

$$\Rightarrow$$  Sum of the ages of B and C = 25 x 2 = 50 years

$$\Rightarrow$$  B + C = 50 ..............(2)

From (1) and (2), A = 10 years

$$\therefore\ $$Age of A = 10 years

Hence, the correct answer is Option B