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Thread: Mortgage calulator HW problem

  1. #1
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    Default Mortgage calulator HW problem

    Hello,

    I am very new to programming and I have hit a stuck point in my code. This is for a mortgage calculator and we have to use the math.pow method. I am getting results, but the results are wrong. The monthly payment is coming out to big.

    Here is what it should be:

    Enter loan amount: 10000
    Enter rate: 4.5
    Enter number years: 3

    The monthly payment is: $297.47


    Here is what I'm getting.

    Enter loan amount: 10000
    Enter rate: 4.5
    Enter number years: 3

    The monthly payment is: $566.06

    Here is my code. I believe my issue is in the math.pow formula. Can someone help my out?



    Scanner in = new Scanner(System.in); // input object

    double loanAmount; //user input
    double interestRate; // user input
    double yearNumber; // user input
    double monthlyPayment; // answer to math
    double finalPayment; // output
    double monthNumber; // year number converted of months
    double monthlyRate; // converted intersted rate


    System.out.print("Enter loan amount: "); // Shows Line to input loan amount
    loanAmount = Double.parseDouble (in.nextLine()); // gets input number


    System.out.print("Enter rate: "); // Shows line to input rate amount
    interestRate = Double.parseDouble (in.nextLine()); // gets input number

    monthlyRate = interestRate * .01; //convert rate into decimal


    System.out.print("Enter number years: "); //Shows line to input number of years
    yearNumber = Double.parseDouble (in.nextLine()); // gets input number

    monthNumber = yearNumber * 12; // total amount of months



    monthlyPayment = Math.pow(1+ interestRate,monthNumber) / (Math.pow(1+interestRate, monthNumber)-1);


    finalPayment = (loanAmount*monthlyRate*monthlyPayment); // gives the payment


    System.out.printf("\nThe monthly payment is: $%.2f", monthlyPayment); // Shows monthly payment


  2. #2
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    Default Re: Mortgage calulator HW problem

    Please use highlight tags when posting code to preserve formatting. Also, please post your code as an MCVE so that we can copy and paste it to run it. I currently don't see a main method or a class definition.

    What happened when you stepped through this with a debugger, or at least added some print statements, to figure out when the program's execution differed from what you expected? What exactly do you mean when you say the output is wrong? Wrong in what way?
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  3. #3
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    Default Re: Mortgage calulator HW problem

    I'm sorry. I don't understand how to use highlight tags. But the answer should be $297.47 in this example and I am getting $566.06. My answer is incorrect meaning the math must be wrong. I can't figure out where it is wrong.

    --- Update ---

    Here is the entire code.

    package assignment2;

    import java.util.Scanner;

    /**
    *
    *
    */
    public class Assignment2 {

    /**
    * @param args the command line arguments
    */
    public static void main(String[] args) {
    // TODO code application logic here

    Scanner in = new Scanner(System.in); // input object

    double loanAmount; //user input
    double interestRate; // user input
    double yearNumber; // user input
    double monthlyPayment; // answer to math
    double finalPayment; // output
    double monthNumber; // year number converted of months
    double monthlyRate; // converted intersted rate


    System.out.print("Enter loan amount: "); // Shows Line to input loan amount
    loanAmount = Double.parseDouble (in.nextLine()); // gets input number


    System.out.print("Enter rate: "); // Shows line to input rate amount
    interestRate = Double.parseDouble (in.nextLine()); // gets input number

    monthlyRate = interestRate * .01; //convert rate into decimal


    System.out.print("Enter number years: "); //Shows line to input number of years
    yearNumber = Double.parseDouble (in.nextLine()); // gets input number

    monthNumber = yearNumber * 12; // total amount of months



    monthlyPayment = Math.pow(1+ interestRate,monthNumber) / (Math.pow(1+interestRate, monthNumber)-1);


    finalPayment = (loanAmount*monthlyRate*monthlyPayment); // gives the payment


    System.out.printf("\nThe monthly payment is: $%.2f", monthlyPayment); // Shows monthly payment
    System.out.println();

    }

    }

  4. #4
    Junior Member Rods's Avatar
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    Default Re: Mortgage calulator HW problem

    convert your Annual interest rate into monthly interest rate. Your annual interest rate here is 4.5 which will become 4.5/100=0.045, 0.045/12=0.00375.

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    Default Re: Mortgage calulator HW problem

    I convert the annual interest rate with
    monthlyRate = interestRate * .01; //convert rate into decimal

    Will that not do the same as /100?

  6. #6
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    Default Re: Mortgage calulator HW problem

    Add some println statements to print out the parts of the expression that the code uses to see which one is not doing what you expect.
    If you don't understand my answer, don't ignore it, ask a question.

  7. #7
    Junior Member Rods's Avatar
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    Default Re: Mortgage calulator HW problem


  8. #8
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    Default Re: Mortgage calulator HW problem

    Do you have an example?

  9. #9
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    Default Re: Mortgage calulator HW problem

    There are 12 months in a year.

    If you eat 120 apples per year, that means you eat 10 apples per month.

    What is your interest per year? Then what is your interest per month?
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  10. #10
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    Default Re: Mortgage calulator HW problem

    I read this before and it helped. I missed the part about monthly rate. so I just added this
    yearRate = interestRate * .01; //convert rate into decimals
    ** monthlyRate = yearRate / 12; // convert rate to month rate

    And now it works correctly. Thanks for your help everyone.

  11. #11
    Junior Member Rods's Avatar
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    Default Re: Mortgage calulator HW problem

    Excellent. Enjoy.

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