How many valentines are exchanged if each of five friends gives a valentine to each of their other friends? Reflect on your solution, compare it with some others listed, and think about how you would solve a similar problem for more people.
You took four snapshots of some geometric shapes that you saw on your train trip around a circular track. You dropped the pictures and got them mixed up, and now you must imagine your trip to put them back in order.
The computer makes up a mystery operation and you have to figure out what it is. Keep entering pairs of numbers for the computer to calculate and try to find the pattern in the answers the computer gives until you think you know what's going on.