A) 10 years
B) 20 years
C) 30 years
D) 40 years
Five years ago ages of A and B are A – 5 , B – 5
So Averge , (A + B)/ 2 = 15
[(A – 5) + (B – 5)]/2 = 15
A + B – 10 = 30
A + B = 40 ……….(i)
Now average ages of A , B and C is 20
( A + B + C)/3 = 20
A + B + C = 60 ……… (ii)
Putting equation (i) into (ii)
40 + C = 60
C = 20
After 10 years C = 20 + 10 = 30