Here’s a little conundrum based on St. Peter’s game. Say I have 11 cans, 5 of which contain tuna and 6 of which contain dog food. If I count off by nines, dropping every ninth can, am I gauranteed to end up with a can of tuna in the end (who wants to eat dogfood)? Hint: There is an easy way to prove this. First put them in alternating order and count off. Then group them together (tuna with tuna, etc.) and count off. Note there are also two ways of counting – either always starting (counting 1) with a can on one of the ends or starting (counting 1) with every tenth can.
