9.2. The age of a certain person in 1988 was equal to the sum of the digits of their birth year. How old was he




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9.2. The age of a certain person in 1988 was equal to the sum of the digits of their birth year. How old was he
Answer: 22.

Solution. The number of years a person has lived is equal to the sum of the digits of a four-digit number, each of which is no more than 9. Therefore, he is no more than 36 years old, and he was born in the 20th century. Let $x$ be the number of tens, $y$ be the number of units in his birth year.

Then, according to his age, we get the equation

$$
1+9+x+y=88-(10 x+y), \text{ or } 11 x+2 y=78
$$

From this, $x=6, y=6$, which means he was born in 1966, and in 1988 he was 22 years old.