The ratio of the ages of a father to that of their ages

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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.

1. 50 yr
2. 60 yr
3. 80 yr
4. 100 yr

Correct Option: B

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