Originally Posted by dhuey
One minor adjustment -- don't forget the 1x miles one gets for charging the convenience fee.
So, if you want more exactitude, instead of 0.0249*P = W*2P, which tells you that you will be paying 1.245 cents per mile obtained this way (provided there are no flat fees to be paid in addition to the percentage one), make it: 0.029*P = W*2.01245P. That will lower the cost per mile ever so slightly. (Don't have a calculator handy, but imagine it means only a couple of $s per 10K of miles.)