Five years ago the average of the ages of A and B was 40 years and now the average of the ages of B and C is 48 years. What will be the age of the B ten years hence?

A. 55 years
B. 56 years
C. 58 years
D. Data inadequate

Let the present ages of A, B and C be a, b and c respectively.

Given, [(a – 5) + (b – 5)] / 2 = 40 => a + b = 90 — (1)
(b + c)/2 = 48 => b + c = 96 — (2)
From (1) and (2), we cannot find b