Another question about calculations

I need to do a slightly more complex calculation than discussed over here http://wp-types.com/forums/topic/need-to-limit-the-number-of-digits-output-from-a-calculation/

Basically, I need to do a calculation like this:

(A – B) / B

And I need it to output as a percentage limited to 2 decimal points.

I've tried to work it out on my own, but haven't had any luck so far.

Any help would be greatly appreciated.

Thanks

Dawson