Question

Three years ago, the average age of a, b and c was 27 years and that of b and c, 5 years ago was 20 years. a’s present age is?

Answer 1

let present age be a, b, and c

three years ago , ages had been = a-3, b-3 , and c-3

their average = a-3 + b-3+c-3 / 3 = 27
                   =  a+b+c-9 = 81
                  = a+b+c = 90            ...........(1)


five years ago , ages had been = b-5 and c-5

their average = b-5 + c-5 /2 = 20
                     = b+c - 10 = 40
                    = b+c = 50            ............(2)

subtracting (2) from (1) gives a = 40 years.