by Dave Youngs.
This month's Puzzle Corner is a classic riddle requiring reasoning to reconcile. (Please forgive the crude alliteration.) While many of you have encountered this riddle before and already know the answer, the riddle probably caused curious consternation (I beg your pardon once more) the first time you saw it. Riddles like the one presented here automatically appeal to a wide variety of people and it's quite likely your students will enjoy puzzling over The Relative Riddle. Although not many riddles are mathematical in nature, this one is, and solving it involves a key concept in the area of mathematics known as set theory.
Before introducing this puzzle to your class, please caution students not to blurt out the answer if they already know it or figure it out before the rest of this class. Doing this will rob other students of the opportunity to think the riddle through and solve it for themselves.
To help your students become better puzzle solvers and mathematical thinkers, it is imperative that you try to build a classroom puzzle and problem-solving ethos that encourages students to work on the problems before being shown any solutions. Doing this builds persistence, one of the most important problem-solving traits. In our current educational climate where getting the correct answer quickly and efficiently often seems more important than developing students' thinking skills, building persistence is often neglected.
I hope that you and your students enjoy this riddle.