This kind of problem can generally be simplified as a line segment with n points evenly distributed (including two endpoints, one is the starting point and the other is the end point). This line segment is divided into n- 1 segments! !

Therefore, the key to adding 1 or subtracting 1 is to distinguish between "points" and "intervals".

If the interval is known, add 1 to find the point; If the "point" is known to find the "interval", subtract 1.

Remember three things, 1. Not counting the two endpoints, there are n-2 points on the line segment.

2. Not counting the starting point, there are n- 1 points on the line segment.

3. Not counting the end point, there are n- 1 points on the line segment.

For example, the problem of planting trees, 100 meters long road, every 10 meters to plant a tree, * * * how much?

Solution: that is, by considering the given conditions of the topic, we can find out whether it is a "point" or an "interval". Obviously, this topic gives an interval of 10, so we planted 10 = 1 1 tree.