Python Version of Homework #3
# Finds out how many months it takes to pay off a $1000 purchase with no downpayment.
rate = .015 # Interest rate of 1.5% per month.
payment = 50 # Monthly payment.
balance = 1000 # How much debt remains.
months = 0 # How many monthly payments have been made so far.
while balance > 0:
thismonthsinterest = balance * rate # How much debt accrues this month
balance = balance + thismonthsinterest - payment
months += 1
print months, ' Interest: $%.2f' % thismonthsinterest, ' Balance: $%.2f' % balance
This gives the output:
1 Interest: $15.00 Balance: $965.00
2 Interest: $14.47 Balance: $929.48
3 Interest: $13.94 Balance: $893.42
4 Interest: $13.40 Balance: $856.82
5 Interest: $12.85 Balance: $819.67
6 Interest: $12.30 Balance: $781.97
7 Interest: $11.73 Balance: $743.70
8 Interest: $11.16 Balance: $704.85
9 Interest: $10.57 Balance: $665.42
10 Interest: $9.98 Balance: $625.40
11 Interest: $9.38 Balance: $584.79
12 Interest: $8.77 Balance: $543.56
13 Interest: $8.15 Balance: $501.71
14 Interest: $7.53 Balance: $459.24
15 Interest: $6.89 Balance: $416.13
16 Interest: $6.24 Balance: $372.37
17 Interest: $5.59 Balance: $327.95
18 Interest: $4.92 Balance: $282.87
19 Interest: $4.24 Balance: $237.11
20 Interest: $3.56 Balance: $190.67
21 Interest: $2.86 Balance: $143.53
22 Interest: $2.15 Balance: $95.68
23 Interest: $1.44 Balance: $47.12
24 Interest: $0.71 Balance: $-2.17
Comments
crywolf on Jan. 27, 2009 4:29 PM
Slight bug there at the end. It's not difficult to fix, though, and I'm guessing you've already seen it.
matt-arnold on Jan. 27, 2009 5:18 PM
Are you talking about the negative balance? I don't see that as a problem.
crywolf on Jan. 27, 2009 5:30 PM
I'd consider it a problem, since balanced owed generally shouldn't be able to go negative. I suppose it depends on the scope of the assignment, although the last paragraph of the description seems to indicate that the last payment should be smaller: "The last payment may be less that $50 if the debt is small, but do not forget the interest." I suppose it all depends on the definition of "may".
arran4 on Feb. 15, 2009 4:15 AM
Perhaps it has uses to know exactly how much was required to pay it off on the last payment?
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