Mathematical Brain Teasers and Logic Puzzles

Why do we create puzzles simply for the pleasure of solving them? After proposing a few theories, Professor Rosenhouse notes that mathematicians love puzzles, especially those that lead to deep mathematical insights. Get warmed up for the series with six brain teasers involving hourglasses, a restaurant order, a biased coin, the numbers on a clock face, and two chessboard scenarios.

Test your wits against the puzzle that likely inspired the famous expression “thinking outside the box.” Then apply this strategy to a variety of brain teasers, involving matchsticks, cards, light switches, and other objects in interesting and puzzling situations. Also ponder the legendary physics exam question: How can you find the height of a building by using a barometer?

First, find a shortcut solution to a classic word problem in algebra. This introduces the episoide’s theme: forget your algebra and use cleverness to solve problems without x’s and y’s. Along the way, you’ll learn that sometimes having too much information can make a problem harder. Also find out why transcontinental flights take longer in one direction than the other (not counting wind effects).

Now turn to logic puzzles, trying to distinguish between knights who only make true statements, and knaves who only tell falsehoods. Start with simple cases. Then introduce tricky “if–then” statements. Next, what if the knight or knave is insane and thus has false beliefs? This makes things trickier! Finally, add a third category: normal people who are sometimes truthful, sometimes not.

Lewis Carroll, author of Alice’s Adventures in Wonderland, wrote a book of logic puzzles for children. Take a crack at some of these fun exercises, which Carroll designed to illustrate the principles of Aristotelian logic. See what you can conclude from such categorical statements as “all wasps are unfriendly, and all puppies are friendly.” Carroll’s syllogisms get progressively more elaborate.

Return to the Island of Knights and Knaves to consider puzzles where asking the right questions is the point of the problem. Work your way up to the famous “heaven or hell” puzzle. Then close with an exercise in coercive logic, devised by noted mathematician and puzzle master Raymond Smullyan. Easy riches hinge on a very simple bargain that sounds too good to be true. Do you accept?