||10 friends run into each other at a bar. We will name them A,B,C,D,E,F,G,H,I AND J.
They all leave at the same time heading for seperate bars. However, A runs into B, C runs into D, E runs into F, G runs into H and I runs into J. These five groups leave again and the same thing keeps happening, but each time running in to someone they have not run into before. How many bars will it take, with each person meeting the others only once, until all of them have met each other again?
Answered by Chris Fisher.