10. (5 points) 3 years ago, Dad's age was 8 times MingMing's age, this year, Dad's age is 5 times MingMing's age, so Dad is $\qquad$ years old this year.
【Analysis】3 years ago, the father's age was $\frac{8}{8-1}$ of the age difference between father and son. This year, the father's age is $\frac{5}{5-1}$ of the age difference. Over the 3 years, the corresponding ratio is $\left(\frac{5}{5-1}-\frac{8}{8-1}\right)$. Using division, we can find the age difference between father and son, and then we can find the father's age this year. According to this, solve the problem.

【Solution】Solution: $3 \div\left(\frac{5}{5-1}-\frac{8}{8-1}\right)$
$$
\begin{array}{l}
=3 \div\left(\frac{5}{4}-\frac{8}{7}\right) \\
=3 \times \frac{28}{3} \\
=28 \text { (years) } \\
28 \times \frac{5}{5-1}=35 \text { ( }
\end{array}
$$

Answer: The father is 35 years old this year.
Therefore, the answer is: 35.