Have I learned all the basic training of mathematics in Volume 2 of grade 6 of primary school

Have I learned all the basic training of mathematics in Volume 2 of grade 6 of primary school

Look at the exam results

A math problem, elementary school grade 6 Volume 2 basic math training p35t4
At the opening ceremony of the school, 40 colored flags will be planted along the 400m track of the playground. Please explain that no matter how, at least two colored flags will be planted, and the distance between them is not more than 10m.

This is based on the drawer principle
You can understand that if the 400 meter runway is a straight line, then every 10 meters a flag, exactly 40
Now the problem is that the runway is closed, which is similar to a circular shape. In the past, the first flag and the last flag overlapped. That is to say, if the 400 runway only needs 39 flags every 10 meters, now there is one more flag. According to the drawer principle, the distance between at least two flags is less than 10