easy combinatorics
Source: flanders '93
September 27, 2005
pigeonhole principle
Problem Statement
The 20 pupils in a class each send 10 cards to 10 (different) class members. [note: you cannot send a card to yourself.]
(a) Show at least 2 pupils sent each other a card.
(b) Now suppose we had pupils sending cards each. For which is the above true? (That is, find minimal or maximal )