Teachers have four kinds of sports in the school sports meeting, and everyone takes part in at least two kinds of sports. So how many teachers do you need to participate to ensure that two people will participate in the sports meeting? This is a question of permutation and combination. Let me give you a detailed step.

4 kinds of projects, a group of 2 kinds, 1 * * with c (2,4 4) = n! /m！ /(n-m)！ = 4! /2! /(4-2)! = 6

So a * * * needs 6+ 1=7 teachers to ensure the same combination.

The formula is the combination of m elements in n elements.

If you don't need to use formulas, then

Let four kinds of sports be ABC D.

A * * * has the following combinations:

AB AC AD BC BD CD

So we need seven teachers.