13. (3 points) The page numbers of the two volumes of "Good Youth" used a total of 888 digits, and the lower volume used 8 more pages than the upper volume. The lower volume of the book has $\qquad$ pages.
13. (3 points) The page numbers of the two volumes of "Good Youth" used a total of 888 digits, and the lower volume used 8 more pages than the upper volume. The lower volume has 170 pages.
【Solution】Solution: The single-digit pages $1 \sim 9$ use a total of 9 digits;
The two-digit pages $10 \sim 99$ use $2 \times 90=180$ digits;
At this point, there are still $888-9-180=699$ digits left,
$$
699 \div 3=233 \text {, }
$$
699 digits can form 233 three-digit numbers,
So the total number of pages in both volumes is:
$$
233+100-1=332 \text { pages, }
$$

Then the number of pages in the lower volume is:
$$
\begin{aligned}
& (332+8) \div 2 \\
= & 340 \div 2, \\
= & 170 \text { (pages). }
\end{aligned}
$$

That is, the lower volume has 170 pages.
The answer is: 170.