What You Need:
- A participant
- 3 dice
- 1 glass
What You Do:
- Let your child fill the glass up about ¾ of the way full with water.
- Hand the three dice to your child.
- Next, have her drop the dice into the glass of water.
- Ask your child to lift the glass above her head.
- Have her to add up the total of the numbers facing down (through the bottom of the glass) and tell her to keep her answer secret.
- Have your child place the glass on a flat surface in front of you.
- Dip the tips of your fingers into the glass of water as if you're sensing the total on the bottom of the dice. During the diversion, add up the total of the numbers featured on the dice that are facing upwards toward you and subtract the total from 21. The difference is your child's sum.
- Press the tips of her fingers to your head and "guess" the sum that your child calculated.
- Teach your child how the trick works and encourage her to try it out on some of her friends.
What's Going On Here?
The secret is in the dice. If you add up the opposing sides of a die, the sum is always seven. Since you are using three dice, the total for the six sides in question will be 21 (because 3 x 7 = 21). All you need to do to "guess" your child's total is add up the numbers on the dice facing upwards and subtract the sum from 21.
For example, if there are three fives facing downwards, then there will be three twos facing upwards. Add the three twos together (for a total of six) and subtract that number from 21 and you'll have the total.