Solutions; If there are X students on duty at a traffic intersection, the middle school will send 4x+78 students on duty.

4x+78-8(x- 1) is less than 8.

4x+78-8(x- 1) is greater than or equal to 4 people ... There are less than 8 people at the last intersection, but not less than 4 people.

20.5 is greater than or equal to x, and x is greater than 19.5.

According to the meaning of the question, x is a positive integer, so x=20

The corresponding middle school * * * Selected Graduates is 158.