Write single digit numbers (1 - 9) on each card making 2 or 3 sets, depending n class size. Distribute at random, one card to each student and the teacher keeps one card. She/he then verbally gives her/his number to the first student. The first student adds his/her number to the teacher's number. They then pass this sum on to their neighbor who adds it to his/her number and likewise passes on the sum. This continues around the classroom until all students have added a number and the sum is very large. Repeat the process, but in the reverse direction, this time with each student subtracting his/her number. If no errors are made, the teacher will receive the original number with which the activity was initiated. This game is both fun and serves as a good mental alertness exercise.