I read a statement that was unclear to me, and was hoping to get some clarification.
It said that given a full binary tree with $n > 2$ leaves, there exists some internal node such that one third to two thirds of all $n$ leaves in the tree are its descendants.
From my understanding, I know each internal node in a full binary tree has 2 children. That said, the whole tree has $2n - 1$ nodes, which means $n - 1$ of them are internal nodes (not leaves).
I can come up with drawn examples where this is always the case, but I am not sure how to formally reason it. Any help would be greatly appreciated.