$\underline{\text { Folklore }}$

At a chamber music festival, six musicians gathered. At each concert, some of the musicians perform, while the others listen from the audience. What is the minimum number of concerts required for each of the six musicians to have listened to (from the audience) all the others?
A total of $6 \cdot 5=30$ auditions are needed. No more than 9 auditions can take place in one concert. Therefore, there must be at least four concerts.

Example: Musicians with numbers (4,5,6), (2,3,6), (1,3,5), and (1,2,4) perform in the concerts.

## Answer

In 4 concerts.