Pail of water, ashtray, matches, bar of soap
Before students arrive:
Choose a number between 10 and 49, for example 15.
Using the bar of soap, write the number you have chosen on the back of your hand.
Now subtract that number from 99.
(For example, 99 - 15 = 84).
When students arrive:
1. Have students choose a number between 50 and 99.
2. Have them add 84 (your answer from above) to that number.
3. Cross out the hundreds digit and add to the units digit.
4. Subtract the answer from the original number.
5. Have one student write his answer on a folded piece
of paper, fold into fourths, and hand it to you.
6. Burn the folded answer in the ashtray.
7. Rub the ashes on your hand, then dip your hand in water.
8. To the students' amazement, the answer "appears" on your hand!
|1. Have students choose a number between 50 and 99.||Let's say the students chose 72.|
|2. Add 84 (your answer from above) to that number.||Then they get 72 + 84 = 156|
|3. Cross out the hundreds digit and add to the units digit.||Cross out the 1 and add it to 56 to get 57.|
|4. Subtract the answer from the original number.||They should get 72 - 57 = 15.|