How old are you?

I picked this up off the Net - if you have a mathematical bent (no rude comments please!), it's not too difficult to see how it works, and as set out it will only work for this year of 2007, but it's a good party trick to have up your sleeve - although you might want to have a calculator about your person to aid the arithmetically challenged. Anyway, here it is -
1. Think of a number between 1 and 9
2. Double it
3. Add 5
4. Multiply the answer by 50
5. If you've already had your birthday this year, add 1757, otherwise add 1756
6. Deduct the 4-digit year of your birth
7. You are now left with a 3-digit number - the first digit is the number you thought of, the other two digits are your age.


Now isn't that clever?