An explorer sets off for a long walk. To start off, he heads south. After he has walked a mile, he sees a bear in the distance, who looks rather hungry, and so he turns to the east.
Another mile on, the explorer spies another bear. So he heads north.
No sooner does he complete his third mile than he finds himself back at the point where he started. Now, what colour were the bears?
Take a chessboard and 31 dominoes. Each of the dominoes is just the right size to cover two squares of the chessboard. Imagine that you cut off the two squares at opposite corners of the board.
Can you cover the mutilated chessboard with the 31 dominoes, without any overlapping? If so, how? If it can’t be done, why not?
Remove one match and move two to leave nine squares.
Make 14 squares using only 8 matches.
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