The Number 3 Trick

Take a number.
Double it.
Add 9.
Subtract 3.
Divide by 2.
Subtract your original number.
Your answer should be 3.

The Number 4 Trick

The same basic trick also works with 4.
Take a number.
Double it.
Add 12.
Subtract the remarkable 4.
Divide by 2.
Subtract your original number.
Your answer should be 4.

The Number 5 Trick

Ask somebody to think of a number and keep it secret.
Then ask that person to double the secret number and then multiply by 5.
Ask for the total.
Whatever the total is, knock off the last digit
and you will have the secret number the person mentally chose at the start.

The Number 37 Trick

There is a three-factor in this one.
Multiply 37 by 3, and you have 111.
Jump up three numbers to 6, and mutliply by 37 again.
You have 222.
Three more and you are at 9.
Multiply by 37 again and you have 333.
This "jumpupthree" routine works all the way up to 27
(27 x 37 = 999).
After that, 37 loses its magic.