From 5bede1d79f1cda165a662e3e194adfbfb0e297eb Mon Sep 17 00:00:00 2001
From: bwoodhoutson <31172910+bwoodhoutson@users.noreply.github.com>
Date: Sat, 19 Aug 2017 21:53:14 -0500
Subject: [PATCH] The original code has the incorrect formula... thus giving
 the incorrect monthly payment.

The original slide from their video has the wrong formula...

The formula should be:

monthlyPayment = P *( I * (1+ I)**N / ((1 + I)**N -1))


(test P = 100,000 // I = 6% // loanDurationInYears = 15years) == should give monthly payment of 843.86

Their original code gave a monthly payment of $5,000 to 6,000...
---
 ...ule4MortgageCalculatorChallengeSolution.py | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/Solutions/Module4MortgageCalculatorChallengeSolution.py b/Solutions/Module4MortgageCalculatorChallengeSolution.py
index ddb9c28..8d6b4a9 100644
--- a/Solutions/Module4MortgageCalculatorChallengeSolution.py
+++ b/Solutions/Module4MortgageCalculatorChallengeSolution.py
@@ -1,4 +1,3 @@
-
 #Declare and initialize the variables
 monthlyPayment = 0
 loanAmount = 0
@@ -7,26 +6,26 @@
 loanDurationInYears = 0
 
 #Ask the user for the values needed to calculate the monthly payments
-strLoanAmount = input("How much money will you borrow? ")
-strInterestRate = input("What is the interest rate on the loan? ")
+strLoanAmount = input("How much money will you borrow?  ")
+strInterestRate = input("What is the interest rate on the loan? (ex 6%=.06)   ")
 strLoanDurationInYears = input("How many years will it take you to pay off the loan? " )
 
-#Convert the strings into floating numbers so we can use them in teh formula
+#Convert the strings into floating numbers so we can use them in the formula
 loanDurationInYears = float(strLoanDurationInYears)
-loanAmount = float(strLoanAmount)
-interestRate = float(strInterestRate)
+P = float(strLoanAmount)
+I = float(strInterestRate)/12
 
 #Since payments are once per month, number of payments is number of years for the loan * 12
-numberOfPayments = loanDurationInYears*12
+N = loanDurationInYears*12
+
 
 #Calculate the monthly payment based on the formula
-monthlyPayment = loanAmount * interestRate * (1+ interestRate) * numberOfPayments \
-    / ((1 + interestRate) * numberOfPayments -1)
+monthlyPayment = P *( I * (1+ I)**N / ((1 + I)**N -1))
 
 #provide the result to the user
 print("Your monthly payment will be " + str(monthlyPayment))
 
 #Extra credit
 print("Your monthly payment will be $%.2f" % monthlyPayment) 
-
+## for this example (Principle = 100,000, Interest = 6%, years = 15,  monthly payment = 843.86)