B was born when A was 4 years 7 months old and C was born when B was 3 years 4 months old. When C was 5 years 2 months old, then their average age was :

Answer: Option D

According to the question,

A - B = 4y 7m . . . . . . . (i)

B - C = 3y 4m . . . . . . . (ii)

(+)  (+)   (+)

A - C = 7y 11m . . . . . . . (ii)

Given :
When, C = 5 years 2 months
∴ A = 13 years 1 month
B = 8 years 6 months
∴ Average of $$\frac{A+B+C}{3}$$
$$=\frac{\text{26 years 9 months}}{3}$$
= 8 years 11 months