I need to calculate the monthly compounding interest in a savings account that is getting a monthly deposit. The variables I have to work with:
monthly savings ( Eg. I deposit $125.75 each month)
months (Eg. I deposit the same for 15 months)
APR (the ANNUAL interest is 5.65%)
Now I need to calculate the total savings amount, which for the given numbers here, the final answer should be $1958.88.
In essence, I am working with A = P(1 + r/12)^(12*t), where P is the amount I deposit * months, r is the APR, and t is the months/12 to get the "how many years"
The catch here is that I can not use the math.pow() as a requirement on the assignment, so my best guess is that I am to calculate it with a for/while loop similar to the following:
public static void main(String[] args)
{
double monthlySavings = 125.75;
double APR = 5.65;
int months = 15;
int monthCount = 0;
double totalSavings = 0;
while (monthCount < months)
{
totalSavings += monthlySavings + (1+APR/12/100);
mothCount++;
}
System.out.printf("Your total savings will be $%.2f\n", totalSavings);
}
The above code is NOT the correct solution, but its the closest i've come. The problem is that I am applying the interest to the monthly savings each time before it accumulates to the total. eg. it adds 125.75*interest for 15 deposits. What it SHOULD do is start with 125.75*interest then add 125.75, and then take the interest of the amount you have total so far, then add 125.75 and take the interest of the total amount again, and so on for the amount of months.
This is probably a lot easier than I am making it out to be, but I have tried for hours with adding different placeholder variables, but I am lacking some crucial concept, please help!
A loop for the number of months
for (int monthNumber = 0; monthNumber < numberOfMonths; monthNumber++)
{
}
then for each each month, add the interest then add the monthly savings. In that order, the other way around you end up with interest on money you just deposited, which is wrong.
totalSavings *= (APR / 12 / 100); //Although I would have separate variable for this
totalSavings += monthlySavings;
you don't really need to keep a month count but I prefer for loops.
After re-reading my question, I had an epiphany.. As I originally thought, the answer was a lot easier than I was making it out to be.
public static void main(String[] args)
{
double monthlySavings = 125.75;
double APR = 5.65;
int months = 15;
int monthCount = 0;
double placeHolder = 0;
double totalSavings = 0;
while (monthCount < months)
{
placeHolder += monthlySavings;
totalSavings = placeHolder * (1+APR/12/100);
placeHolder = totalSavings;
monthCount++;
}
System.out.printf("Your total savings will be $%.2f", totalSavings);
}
Related
im calling a function to help work out a second calculation but it complies but dosnt return correct answer
tired a few different things but breaks codes so more then likely completely wrong
9. This question involves writing two functions.
a. The interest on a loan is currently 2.4% (0.024). If you take a £9000
loan to day you will pay 9000 * 0.024 ( £216) for a year. Start by writing a
function called calculateInterest which takes the loanAmount
(which can be any number not just 9000) as a float and a second argument
interestRate (also float can be any faction) which is the interest rate
for the loan. It should return a float which is the Interest (£216 in the
example above).
b. When calculateInterest works write a function called HW2I. (I=capital i)
This takes 2 float arguments. The original loan amount (float) and years
(an int) which is the number of years the loan will operate over (say 35).
Each year the interest is calculated (via a call to the calculateInterest
function). Interest is then added to the loan amount. This value (loan+
interest) is the new loan amount. Write the function HW2I. Don’t forget to
test it yourself to make sure it works correctly. Here is the pseudo code.
To HW2I ( loan, intreastRate , years )
Repeat with year = 1 to years
adjustedLoan = loan + calculateInterest( loan , intreastRate )
loan = adjustedLoan
end repeat
return loan
public float calculateInterest(float loanAmount, float interestRate) {
float intrest;
intrest = loanAmount * interestRate;
return intrest;
}
public float HW2I(float loan, int years) {
for (int i = 0; i <= years; i = i++) {
loan = loan + calculateInterest(9000, 0.24);
}
return (loan);
}
I guess we go to the same university because I have the exact same question so here's the answer:
public float calculateInterest(float loanAmount, float interestRate) {
float interest = (loanAmount * interestRate);
{
return interest;
}
}
public float HW2I(float loanAmount, float interestRate, int years) {
for (int i = 0; i < years; i++) {
float newLoanAmount = loanAmount + calculateInterest(loanAmount, interestRate);
loanAmount = newLoanAmount;
}
return loanAmount;
}
Good luck!
For the explanation:
The first method only asks us to calculate the interest, which is done by multiplying the loanAmount and the interestRate together. After, we return the interest.
For the second function, the pseudo code shows us that we need 3 arguments, which are float loanAmount, float interestRate and int years. It also says "Repeat with year= 1 to years" meaning we need to use iteration, so we do the for(int i= 0; i< years; i++ part. If we look back at the question we need a newLoanAmount which is the first loanAmount + a call to the first method, which is calculateInterest(loanAmount, interestRate). Now the loanAmount becomes the newLoanAmount, kind of replacing the value of the loanAmount before. Because the value has changed, we need to return loanAmount.
I hope this helps further and apologises if it isn't a great explanation; I started learning Java 2 months ago.
There is a table with purchase details. Let say, an item "chocolate" is sold 1500 in total for past one week (one week from yesterday). Yesterday it was sold 230 in total. I have counts for per day and per week.
is it possible to get variance/standard deviation by taking an average on count past week and compare with yesterday count. basically variance / sd on avg(1500) and 230. Please suggest if its correct way to and advice on how to do it in java.
Thanks in advance.
Please take a look at this answer:
https://stackoverflow.com/a/36186227/8310211
Maybe you want to modify it to use a double[] array as input:
public static double stdDev(double[] inputArray) {
double sum = 0;
double sq_sum = 0;
for (int i = 0; i < inputArray.length; ++i) {
double ai = inputArray[i];
sum += ai;
sq_sum += ai * ai;
}
double mean = sum / inputArray.length;
double variance = sq_sum / inputArray.length - mean * mean;
return Math.sqrt(variance);
}
I have adopted the for loop, to calculate the salary of each month based on two factors: a fixed salary of $50000 and an additional $550/hr on extra hours worked in a month. The latter variable evidently varies per month, and so I adopted the scanner class to receive the input of each month. (All required parameters prior to my loop have been adequately defined)
My loop looks something like this:
for(int month = 1; month <= 12; month++){
System.out.print("How many extra hours did you work this month?");
double extraHoursPerMonth = scan.nextInt();
double bonusSalary = extraHoursPerMonth*bonusSalaryPerHour;
double totalMonthlySalary = basicSalary + bonusSalary;
System.out.println("Your salary for this month is $" + totalMonthlySalary);
When run, the total salary for each month is calculated successfully. How then do I proceed to find the annual salary?
I can not find any code I can use, to sum up, the monthly salaries previously calculated into a final sum and I feel like I'm up against a brick wall. I would appreciate any pointer, hints or advice on how to move forward.
You would have to create a variable outside your for loop and add up the monthly salary for every iteration e.g.
int annualSalary = 0;
for(int month = 1; month <= 12; month++){
System.out.print("How many extra hours did you work this month?");
double extraHoursPerMonth = scan.nextInt();
double bonusSalary = extraHoursPerMonth*bonusSalaryPerHour;
double totalMonthlySalary = basicSalary + bonusSalary;
System.out.println("Your salary for this month is $" +
totalMonthlySalary);
}
System.out.println("Your annul salary for this year is $" + annualSalary);
If you want the annual salary you can get it by multiplying the monthly salary by 12.
double anualSalary = basicSalary*12;
If you want the overall salary you should declare a variable after the declaration of anualSalary and before the for loop.
double overalSalary = anualSalary;
And then add the bonus salary in each loop of the for cycle.
...
overalSalary += bonusSalay;
...
My problem is: Suppose that one credit hour for a course is $100 at a school and that rate increases 4.3% every year. In how many years will the course’s credit hour costs tripled?
The rewrote this simple code many times, but just can't seem to get it.
I think i'm going about this the wrong way..
import java.util.Scanner;
public class MorenoJonathonCreditHourCostCalculator {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
double cost = 100;
int years=0;
double sum=200;
double total;
while (cost >= sum) {
total = cost + 4.03;
++years;
}
System.out.println("The tuition will double in " + years + " years");
}
}
A rate increase of 4.3% means that in every step, the value is 4.3% bigger than the previous value. This can be described by the following formula:
V_n+1 = V_n + (V_n * 4.3%)
V_n+1 = V_n + (V_n * 0.043)
V_n+1 = V_n * (1 + 0.043)
V_n+1 = V_n * 1.043
In Java this boils down to simply cost *= 1.043;
You first stated " In how many years will the course’s credit hour cost tripled", but in your program you actually check for when it has doubled.
I assume you want to calculate the triple cost, so your program should now look something like this:
public static void main(String[] args) {
double cost = 100;
double tripleCost = 3 * cost;
int years = 0;
while(cost < tripleCost) {
cost *= 1.043;
years++;
}
System.out.println("It took " + years + " years.");
}
Which gives the following output:
It took 27 years.
I am not sure why you are adding to cost since it is a multiplication function:
FV(future value) = PV(present value) (1+r)^n
300 = 100(1.043)^n where you are looking for 'n'
Set up a while loop that operates while the future value is under 300 and adds to 'n'.
I am currently trying to develop a compound interest calculator that includes monthly contributions. I have successfully been able to get the compound interest calculation working without the monthly contributions using the following line of code, but cannot figure out what the formula should be when adding monthly contributions.
double calculatedValue = (principalValue * Math.pow(1 + (interestRateValue/numberOfCompoundsValue), (termValue * numberOfCompoundsValue)));
When trying to get the calculated value with contributions I changed the way this is done. See the following code how I approached this.
//The starting principal
double principalValue = 5000;
//Interest rate (%)
double interestRateValue = 0.05;
//How many times a year to add interest
int numberOfCompoundsValue = 4;
//The number of years used for the calculation
double termValue = 30;
//The monthly contribution amount
double monthlyContributionsValue = 400;
//How often interest is added. E.g. Every 3 months if adding interest 4 times in a year
int interestAddedEveryXMonths = 12/numberOfCompoundsValue;
//The total number of months for the calculation
int totalNumberOfMonths = (int)(12 * termValue);
for(int i = 1; i <= totalNumberOfMonths; i++)
{
principalValue += monthlyContributionsValue;
if(i % interestAddedEveryXMonths == 0)
{
principalValue += (principalValue * interestRateValue);
}
}
I figured this should do what I am after. Every month increase the principal by the contribution amount and if that month equals a month where interest should be added then calculate the interest * the interest rate and add that to the principal.
When using the values above I expect the answer $355,242.18 but get $10511941.97, which looks better in my bank account but not in my calculation.
If anyone can offer me some help or point out where I have gone wrong that would be much appreciated.
Thanks in advance
Your problem is here:
principalValue += (principalValue * interestRateValue);
You're adding a full year's interest every quarter, when you should be adding just a quarter's interest. You need to scale that interest rate down to get the right rate.
Here's an example:
class CashFlow {
private final double initialDeposit;
private final double rate;
private final int years;
private final double monthlyContribution;
private final int interestFrequency;
CashFlow(double initialDeposit, double rate, int years,
double monthlyContribution, int interestFrequency) {
if ( years < 1 ) {
throw new IllegalArgumentException("years must be at least 1");
}
if ( rate <= 0 ) {
throw new IllegalArgumentException("rate must be positive");
}
if ( 12 % interestFrequency != 0 ) {
throw new IllegalArgumentException("frequency must divide 12");
}
this.initialDeposit = initialDeposit;
this.rate = rate;
this.years = years;
this.monthlyContribution = monthlyContribution;
this.interestFrequency = interestFrequency;
}
public double terminalValue() {
final int interestPeriod = 12 / interestFrequency;
final double pRate = Math.pow(1 + rate, 1.0 / interestPeriod) - 1;
double value = initialDeposit;
for ( int i = 0; i < years * 12; ++i ) {
value += monthlyContribution;
if ( i % interestFrequency == interestFrequency - 1 ) {
value *= 1 + pRate;
}
}
return value;
}
}
class CompoundCalc {
public static void main(String[] args) {
CashFlow cf = new CashFlow(5000, 0.05, 30, 400, 3);
System.out.println("Terminal value: " + cf.terminalValue());
}
}
with output:
run:
Terminal value: 350421.2302849443
BUILD SUCCESSFUL (total time: 0 seconds)
which is close to the $355k value you found.
There are a number of different conventions you could use to get the quarterly rate. Dividing the annual rate by 4 is a simple and practical one, but the pow(1 + rate, 1 / 4) - 1 method above is more theoretically sound, since it's mathematically equivalent to the corresponding annual rate.
After some brief testing I've come to the conclusion that either you have:
miscalculated the value you want ($355,242.18)
OR
incorrectly asked your question
The calculation you've described that you want ($5000 start + $400 monthly contributions for 30 years + interest every 3 months) is found by the code you've provided. The value that it gives ($10,511,941.97) is indeed correct from what I can see. The only other suggestions I can offer are to only use double if you need to (for example termValue can be an int) AND when ever you know the value is not going to change (for example interestRateValue) use final. It will help avoid any unforeseen error in larger programs. I hope this helps you figure out your interest calculator or answers any questions you have.
static void Main(string[] args)
{
double monthlyDeposit;
double rateOfInterest;
double numberOfCompounds;
double years;
double futureValue = 0;
double totalAmount = 0;
Console.WriteLine("Compound Interest Calculation based on monthly deposits");
Console.WriteLine("Monthly Deposit");
monthlyDeposit = Convert.ToDouble(Console.ReadLine());
Console.WriteLine("Rate Of Interest");
rateOfInterest = Convert.ToDouble(Console.ReadLine());
Console.WriteLine("Number of Compounds in a year");
numberOfCompounds = Convert.ToDouble(Console.ReadLine());
Console.WriteLine("Number of year");
years = Convert.ToDouble(Console.ReadLine());
futureValue = monthlyDeposit;
for (int i = 1; i <= years * 12; i++)
{
totalAmount = futureValue * (1 + (rateOfInterest / 100) / 12);
if (i == years * 12)
futureValue = totalAmount;
else
futureValue = totalAmount + monthlyDeposit;
}
Console.WriteLine("Future Value is=" + futureValue);
Console.ReadLine();
}
//Output
Compound Interest Calculation based on monthly Deposits
Monthly Deposit
1500
Rate Of Interest
7.5
Number of Compounds in a year
12
Number of year
1
Future Value is=18748.2726237313