Answer:
For the sum of the digits of Michelle’s father to drop to 1/3 of its’ former value, the second digit must go from 9 to 0, in one year.
Thus, if he is 39 this year, the sum of the digits of his age will be 12. Next year, when the sum of the digits would be 4+0, or 4, then the digits of his age would be 1/3rd of their former value.
Therefore, he is 39, and will be 40 next year
Explanation: