Discussion

Explanation:

At present father is thrice son's age.
∴ Let the present ages of father and son be 3x and x.

5 years ago, ages of father and son will be 3x - 5 and x - 5 respectively.
5 years ago, father was four times his son's age.

⇒ $\frac{3\mathrm{x}-5}{\mathrm{x}-5}$ = $\frac{4}{1}$

⇒ 3x - 5 = 4x - 20

⇒ 15 = x

∴ Present age of son = x = 15 and present age of father 3x = 45

⇒ Sum of their present ages = 15 + 45 = 60

Hence, 60

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