A is as much younger than B as he is older then C. If the sum of B's and C's age is 40 years. Find the age of A.?

Age of C < Age of A < Age of B
From question,
A = C + x ....(i)
B = A + x ....(ii)
From equation (i) and (ii)
A - B = C - A
⇒ 2A = B + C
⇒ A = (B + C) / 2
Given that sum of the ages of B and C is 40 years.
So, A = (B + C) / 2 = 40/2 = 20 Years