2. This year, the son and daughter are so many years old that the product of their ages is 7 times less than the father's age. And in three years, the product of their ages will already be equal to the father's age. Find the father's age.
Answer: 21 years

Solution. Let $n$ be the son's age, $m$ be the daughter's age, then the father's age is $7 m n$. In three years, the son's age will be $n+3$, the daughter's age will be $m+3$, and the father's age will be $7 \mathrm{mn}+3$, and according to the condition, the equation $(n+3)(m+3)=7 m n+3$ will be satisfied. After combining like terms and canceling by 3, we get: $2 m n-n-m=2$. Multiply the last equation by 2 and represent it as: $(2 m-1)(2 n-1)=5$.

Thus, $2 m-1=5, 2 n-1=1$ (or vice versa), so $m=3, n=1$ and, therefore, $7 m n=21$. That is, currently the son and daughter are 1 year and 3 years old (or vice versa), and the father is 21 years old.