Easy when you know how.

So, how does the the age trick which I posted about on July 5th work? Well, if you really wanted to know someone's age, and didn't want to ask them straight out, the easy way would be to find out their year of birth and then deduct that from 2007 - or 2006 if they haven't yet had their birthday this year.

So, we start with a number between 1 and 9 - we don't know what it is, so call it N.
Double it, so it becomes 2N
Add 5, so it is now 2N+5
Multiply by 50, so it becomes 50(2N+5) = 100N+250
Add 1757 or 1756, depending on whether or not you've had your birthday this year so we now have 100N+ 2007 or 100N + 2006
Deducting your year of birth gives us 100N + your age.

Et voilà!