[Tutor] Hooked on innumeracy....

[kromag@nsacom.net]

I have been attempting to make a little amortization calculator:

-----------------begin mort--------------------

def mort(cash,interest, payment):
	count=1
	bait=cash #retain the original amount for final calucation of total 
interest.
	screwing=interest/12
	interest=screwing+1
	try:
		while cash > payment:
			cash= cash * interest
			cash = cash - payment
			count=count +1
	finally:
		ouch=payment * count + cash # number of payments * payment 
amount + remainder
		print `count` + ' payments of ' + `payment` + ' each.'	
		print 'Plus one payment of ' + `cash`
		print `ouch -bait ` + ' total screwing.'

-------------------end mort---------------------

Now I don't have any idea if my math is right here. It seems logical to me, 
but then, I majored in english and drama.

I get the following weirdness when I attempt to use it:

---------------begin weirdnesss------------------

>>> from kersplort import mort
>>> mort(4000,0.07,250.00)
17 payments of 250.0 each.
Plus one payment of 210.26436268423424
460.26436268423458 total screwing.
>>> mort(4000,0.07,350.00)
12 payments of 350.0 each.
Plus one payment of 300.00544031562856
500.00544031562822 total screwing.
>>> mort(4000,0.07,150.00)
30 payments of 150.0 each.
Plus one payment of 10.313364085220485
510.3133640852202 total screwing.
>>> 
---------------end weirdness---------------------

You'll note that the amount of screwing (total interest payments) seems to be 
nonlinear with the payment amount. What am I missing here? I fully admit to 
being an arithmetic moron, so flame away! :-)