There are three loops in a tangle of rope. How many are independent, and how many are interlocked? Two knights stand on a chessboard. How many other knights must you add so that each square is occupied or threatened by a knight? Among six seemingly identical drawings of mandalas, each rotated by multiples of 60 degrees, one is different. Which is it, and why? Challenge yourself with these mind-benders, brainteasers, and puzzles. Each of them has been...