The ratio of the ages of a father to that of their ages (in years) is 1000, then find the father's age after 10 yr.

Let the age of father = 5k
and the age of son = 2k
According to the question,
5k x 2k = 1000
⇒ 10k² = 1000
⇒ k² = 100
∴ k = √100 = 10
∴ Father's age after 10 yr = (5k + 10)
= 5 x 10 + 10
= 60 yr