by Dave Youngs
This month's activity is a modification of a puzzle originally posed by Lewis Carroll, author of Alice's Adventures in Wonderland. Carroll was the pen name of the Oxford mathematician, Charles L. Dodgson, who in addition to his children's stories, invented games and puzzles and produced scholarly mathematical works.
In this puzzle you are challenged to take ten pennies, which are originally arranged in two rows of five and rearrange them into five rows, each having four pennies. While this may seem impossible at first glance, there are several solutions. While most students will probably begin to attack this problem by trial and error, it should soon become apparent that each penny must be counted in more than one row. This mathematical insight is necessary to solve the puzzle.
Before introducing this puzzle to your students, you might want them to do a related Puzzle Corner activity, Are All Sides Equal?