MathDB

6

Part of 2005 France Pre-TST

Problems(1)

French pre-TST-2004/2005 #6

Source: Me

12/20/2004
On each unit square of a 9×99 \times 9 square, there is a bettle. Simultaneously, at the whistle, each bettle moves from its unit square to another one which has only a common vertex with the original one (thus in diagonal). Some bettles can go to the same unit square. Determine the minimum number of empty unit squares after the moves. Pierre.
analytic geometry