Here is a UK maths trick that may stump you.
1. Grab a calculator. (You won't be able to do this one in your head, Too late.)
2. Key in the first three digits of your home phone number (NOT the areacode)
3 Multiply by 8
4. Add 1
5. Multiply by 250
6. Add the last 3 digits of your phone number
7. Add the last 3 digits of your phone number again.
8. Subtract 250
9. Divide number by 2
>>> Do you recognize the answer?