Maths Olympiad Prep

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Combinatorics Difficulty 5.7 AIME, harder Prove it

On an infinite chessboard, two black checkers are placed on two diagonally adjacent black squares.

Can one additionally place some number of black checkers and one white checker on this board in such a way that the white checker can capture all the black checkers, including the two initially placed, in one move?

Solution

When a black checker is taken, the white checker moves an even number of verticals. Therefore, after the white checker takes the first black one, it will always be an even number of verticals away from the second black checker. Consequently, it cannot take it.

## Answer

It is not possible.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.