More fun with numbers -- the telephone game

A math teacher in real life, Andrée was complimentary about my most recent post about happy numbers.

Thus encouraged, although I knew I was pushing my luck, I was brave enough to try this brain teaser that I stumbled on at this site.

The directions on the original site call for using a calculator. Andrée, if you let your students try this, I hope you'll insist on pencil and paper instead -- it's the Curmudgeon in me.

Anyway, here's the deal:

1. Key in the first three digits of your phone number (not the area code -- what we mature individuals call the 'exchange')

2. Multiply by 80

3. Add 1

4. Multiply by 250

5. Add the last 4 digits of your phone number (yes, this is designed for seven digit phone numbers)

6. Add the last 4 digits of your phone number again

7. Subtract 250

8. Divide number by 2

The answer should look very familiar.

I tried it on three different phone numbers... and it worked each time.