An improbable game of darts
Tony Crilly, Stephen Suen · The Mathematical Gazette · 1987
The general utility of the ‘pigeon hole principle’ (that if n + 1 pigeons are placed in n boxes one of the boxes contains more than one pigeon!) is neatly illustrated by the problem of showing that: If seven darts land on a dartboard in any configuration whatsoever, there will always be two darts which are not more than a distance of one radius apart .