Twenty years ago, this puzzle appeared on a test administered to top-tier math students from 16 countries around the world. Only 10% of test takers got it right. In the U.S., only 4% managed to ...

Brain teasers are one of the best puzzles to test the sharpness of the brain. Readers must think creatively to solve brain teasers. Brain teasers present these challenges as picture puzzles, math ...