Don’t have a calculator? Don’t worry. Just paste this code into Python and let Python do all the work.
from math import log
compound_or_simple = input("simple or compound interest? (s/c)")
if compound_or_simple == "s":
what_to_find = input("Do you want to calculate time, interest, rate or principal? (t/i/r/p) ")
if what_to_find == "t":
i = float(input("How much interest has been earned in dollars? "))
r = float(input("What is the rate of interest as a percentage? "))/100
p = float(input("What was the principal? "))
time = i/r/p
print("The investment was %.2f years." % time)
elif what_to_find == "i":
r = float(input("What is the rate of interest as a percentage? "))/100
p = float(input("What was the principal? "))
t = float(input("How long was the investment in years? "))
interest = r*p*t
print("The investment earned $%.2f in interest." % interest)
elif what_to_find == "r":
p = float(input("What was the principal? "))
t = float(input("How long was the investment in years? "))
i = float(input("How much interest has been earned in dollars? "))
rate = i/p/t
print("The investment rate of interest was %.2f percent." % (rate*100))
elif what_to_find == "p":
r = float(input("What is the rate of interest as a percentage? "))/100
i = float(input("How much interest has been earned in dollars? "))
t = float(input("How long was the investment in years? "))
principal = i/r/t
print("The amount of money originally invested was $%.2f." % principal)
else:
print("Unrecognized input, try again!")
elif compound_or_simple == "c":
what_to_find = input("Do you want to calculate time, interest, rate or principal? (t/i/r/p) ")
n = int(input("How many compounding periods per year? "))
if what_to_find == "t":
i = float(input("How much interest has been earned in dollars? "))
r = float(input("What is the rate of interest as a percentage? "))/100
p = float(input("What was the principal? "))
time = log((p+i)/p)/(n * log(1 + r/n))
print("The investment was %.2f years." % time)
elif what_to_find == "i":
r = float(input("What is the rate of interest as a percentage? "))/100
p = float(input("What was the principal? "))
t = float(input("How long was the investment in years? "))
interest = p*((1 + r/n)**(n*t) - 1)
print("The investment earned $%.2f in interest." % interest)
elif what_to_find == "r":
p = float(input("What was the principal? "))
t = float(input("How long was the investment in years? "))
i = float(input("How much interest has been earned in dollars? "))
rate = n*(((p+i)/p)**(1/(n*t)) - 1)
print("The investment rate of interest was %.2f percent." % rate)
elif what_to_find == "p":
r = float(input("What is the rate of interest as a percentage? "))/100
i = float(input("How much interest has been earned in dollars? "))
t = float(input("How long was the investment in years? "))
principal = i / ((1 + r/n)**(n*t) - 1)
print("The amount of money originally invested was $%.2f." % principal)
else:
print("Unrecognized input, try again!")
else:
print("Unrecognized input, try again!")
