13. (15 points) Master Wang originally planned to start from point $A$ on a circular road with a circumference of 400 meters, and install a street lamp every 50 meters. Each lamp requires digging a hole to bury the lamp post.
（1）According to the original plan, how many holes does Master Wang need to dig?
（2）After digging all the holes according to the original plan, Master Wang felt that the distance between the street lamps was too far, and decided to install a street lamp every 40 meters starting from point $A$. In this case, how many more holes does Master Wang need to dig?
【Analysis】(1) Divide 400 by the interval of 50 meters;
(2) Divide 400 by 40 to find the total number of holes to be dug, then find the least common multiple of 50 and 40, which is 200, so the number of holes that do not need to be moved is $400 \div 200=2$, so the number of additional holes needed is: $400 \div 40-2=8$ (holes).

【Solution】(1) $400 \div 50=8$ (holes)
Answer: According to the original plan, Master Wang needs to dig 8 holes.
(2) The least common multiple of 50 and 40 is 200
$$
\begin{array}{l}
400 \div 40-400 \div 200 \\
=10-2 \\
=8 \text { (holes) }
\end{array}
$$

Answer: Master Wang still needs to dig 8 more holes.
【Comment】This problem examines the tree planting problem, the knowledge point is: the number of trees planted = the number of intervals (when planting in a circle), the difficulty of this problem is to determine the number of trees that do not need to be moved.