8. (6 points) My sister is 26 years old this year, and my younger sister is 18 years old this year. When the sum of their ages was 20, my sister was $\qquad$ years old.
8. (6 points) The younger sister is 18 years old this year, and the older sister is 26 years old this year. When the sum of their ages was 20, the older sister was 14 years old.
【Solution】Solution: $(20+8) \div 2$,
$$
\begin{aligned}
& =28 \div 2, \\
= & 14 \text { (years old); }
\end{aligned}
$$

Answer: When the sum of their ages was 20, the older sister was 14 years old.
Therefore, the answer is: 14.