It's really not hard to stump me since math was one of my worst subject.
Personally I would like to know who came up with this.
1. Grab a calculator
2. Key in the first three digits of your phone number (NOT YOUR 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?