Got the first one as it made its way around the Internet via e-mail. It ended up in the hands of Robin Ollerhead, a friend of our family's and Professor Emeritus in the physics department at the University of Guelph. He took the first trick and made one of his own. They're both reproduced here:
Here's the original:
1 GRAB A CALCULATOR. (YOU WON'T BE ABLE TO DO THIS ONE IN YOUR HEAD).
2 KEY IN THE FIRST THREE DIGITS OF YOUR PHONE NUMBER (NOT THE AREA CODE).
3 MULTIPLY BY 80.
4 ADD 1.
5 MULTIPLY BY 250.
6 ADD THE LAST 4 DIGITS OF YOUR PHONE NUMBER.
7 ADD THE LAST 4 DIGITS OF YOUR PHONE NUMBER AGAIN!
8 SUBTRACT 250.
9 DIVIDE NUMBER BY 2.
DO YOU RECOGNIZE THE ANSWER?
Here's Robin's:
1. Grab a calculator.
2. Key in the first three digits of your telephone number (not the area code).
3. Multiply by 400.
4. Add 2.
5. Multiply by 75.
6. Take the last 4 digits of your telephone number, multiply by 2, and add to your previous answer.
7. Take the last 4 digits of your telephone number, subtract 150, and add to your previous answer.
8. Divide this rather large number by 3.
What have you got?