# [Tutor] Concerning Programming Exercise #6 of Chapter 2 of Python Programming John Zelle Textbook

Mark Tolonen metolone+gmane at gmail.com
Wed Jan 21 04:18:11 CET 2009

```Since you are updating the principal value each year, use the following to grow the principal by the interest rate each year:

principal = principal * (1 + apr)

-Mark
"bob gailer" <bgailer at gmail.com> wrote in message news:49761FDC.5020800 at gmail.com...
Donna Belle Ibarra wrote:
Hi! I need help with program exericse #6 entitled "Futval.py" which is a program that computes the value of an investment carried 10 years into the future.

This is the coding I have.. yet it does not seem to spit out the correct numbers (Am I using an incorrect equation?)

Take a look at http://en.wikipedia.org/wiki/Time_value_of_money#Present_value_of_a_future_sum for the various formulas. I am not sure which applies in your case.

def main():
print "This program calculates the future value"
print "of a 10-year investment."

principal = input("Enter the amount invested each year: ")
apr = input("Enter the annual interest rate: ")
years = input("Enter the number of years: ")

for i in range (1, years + 1):
principal = principal * (1 + apr)**i
print "The value in", i, " years is:", principal

main()

The output is suppose to appear like this:

This program calculates the future value of a 10-year investment.
Enter the amount invested each year: 100.00
Enter the annual interst rate: 0.05
Enter the number of years: 10
The value in 1 years is 105.0
The value in 2 years is 215.25
The value in 3 years is 331.0125
The value in 4 years is 452.563125

And so on..

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--
Bob Gailer
Chapel Hill NC
919-636-4239

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