Answer:
39
Step-by-step explanation:
I assume the father's age is a 2-digit number. He is not 9 years old or younger, and he is not 100 years old or older.
The sum of the digits of a two-digit number goes up by 1 from one number to the next unless the number ends in 9.
For example, from 17 to 18, the sum of the digits goes from 8 to 9.
If the number ends in 9, for example, 29, the digits add to 11. Then the next number is 30, and now the sum of the digits is 3, which is less than 11.
The father's age now is a number whose sum of digits is not only greater than the sum of the digits next year, but it is 3 times greater.
Let's look at 2-digit number and the next number and the sum of their digits.
19, 20; sums: 10, 2; 10/2 = 5, not 3
29, 30; sums: 11, 3; 11/3 ≠ 3
39, 40; sums: 12, 4; 12/4 = 3
Answer: The father is 39 years old.
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