PRIME NUMBER SORTING GAME The team is given a bunch of sealed envelopes, each with a number printed on it. In each prime numbered envelope is a golden ticket. In each composite numbered envelope is a red ticket. Your job is to open all the prime numbered envelopes but not the composite numbered envelopes, which you must instead give to the Ticket Taker, unopened. For each prime numbered envelope you open, you get the golden ticket inside. If by mistake you give a prime numbered envelope to the Ticket Taker, he keeps the golden ticket. For each composite numbered envelope you turn in unopened, he'll take out the red ticket and give you the golden ticket. If by mistake you open it, you're stuck with the red ticket. Your final prize/rank is determined by how many golden tickets you collect. Students should play as a single team. If playing for prizes, a list can be posted ahead of time. For example, if all 99 numbers from 2 to 100 are used, the prizes might be as follows: 80 tickets -- smalest prize 90 tickets -- a little better prize 95 tickets -- medium prize 98 tickets -- good prize 99 tickets -- something really worth playing for Or they can play for "prime number hunter" ranks, or military ranks or aristocratic titles or whatever. If you want to do this activity, I'll supply the envelopes. The idea is for them to understand in elementary terms what a prime number is, e.g., a number is prime if it can't be shared equally among any number of people greater than 1, and for them to find effective strategies for sorting into primes and composites. Also, it is a good activity for getting students to talk to each other and compare ideas, since if they are to make few mistakes, they will need to form a consensus before opening or hading over each envelope.