Mystify Your Friends...

Student library worker Abe Burnsworth shared the following mathematical puzzle:

Grab a calculator and enter the first 3 digits of your phone number (not your area code);
Multiply by 80;
Add 1;
Multiply by 250;
Add the last 4 digits of your phone number;
Add the last 4 digits of your phone number again;
Subtract 250;
and divide it all by 2.
You should recognize the result.

For more baffling math action, check out Kepler's conjecture: How some of the greatest minds in history helped solve one of the oldest math problems in the world (QA 93 S97 2003) or Anno's math games (793.7 A6154). And if you can figure out how this trick works, please tell us!