According to my windows calculator program: 22/7 = 3.1428571428571428571428571428571
According to my memory: pi = 3.1412565359
So, that's accurate in the first two digits, with an error factor of roughly 0.04%
Archimedes' method for approximating pi
Formula that gives the n'th hexadecimal digit of pi without reference to any of the previous n-1 digits
OK, so the second one isn't an approximation... it's actually pi. Anyway, that's what I could come up with in 15 minutes at work. Thanks, Steve!