10. (10 points) This year, the sum of Jia and Yi's ages is 70 years. Several years ago, when Jia was as old as Yi is now, Yi's age was exactly half of Jia's age. How old is Jia this year?

保留源文本的换行和格式如下：

10. (10 points) This year, the sum of Jia and Yi's ages is 70 years. Several years ago, when Jia was as old as Yi is now, Yi's age was exactly half of Jia's age. How old is Jia this year?
【Analysis】According to the problem, we can derive: several years ago, Yi's age was half of Yi's age this year, so this year Jia's age is 1.5 times (1+0.5=1.5) of Jia's age several years ago, so this year Jia's age is 1.5 times that of Yi's age this year. Furthermore, based on the sum of Jia and Yi's ages this year being 70 years. We can find out how old Jia is this year.

【Solution】Since when Jia's age was the same as Yi's current age, Yi's age was exactly half of Jia's age, this year Jia's age is: $1+0.5=1.5$ times that of Jia's age several years ago, so this year Jia's age is 1.5 times that of Yi's age this year,
$$
\begin{array}{l}
70 \div(1+1.5) \times 1.5 \\
=70 \div 2.5 \times 1.5 \\
=28 \times 1.5 \\
=42 \text { (years old) }
\end{array}
$$

Answer: Jia is 42 years old this year.