All of n elderly dons initially know 1 (different) item of gossip. There are n items of gossip in total. One don can telephone another don and, during the telephone call, each will reveal all the gossip they know so far to the other.

What is the minimum number of telephone calls required so that all the dons know all n items of gossip?


(Yep, I'm back from university. The course is great everyone. Good to see the board is still up and running with some familiar names around )