I am unable to where the error in this is.

Question

There's this problem:
You take a loan from a friend and need to calculate how much you will owe him after 6 months.
You are going to pay him back 10% of the remaining loan amount each month.
Create a program that takes the loan amount as input, calculates and outputs the remaining amount after 6 months.

Sample Input:
20000

Sample Output:
10628

Here is the monthly payment schedule:
Month 1
Payment: 10% of 20000 = 2000
Remaining amount: 18000
Month 2
Payment: 10% of 18000 = 1800
Remaining amount: 16200
Month 3:
Payment: 10% of 16200 = 1620
Remaining amount: 14580
Month 4:
Payment: 10% of 14580 = 1458
Remaining amount: 13122
Month 5:
Payment: 10% of 13122 = 1313
Remaining amount: 11809
Month 6:
Payment: 10% of 11809 = 1181
Remaining amount: 10628.

I provided this solution:

import java.util.Scanner;

public class Program
{
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int amount = scanner.nextInt();
//your code goes here

int m, payment;
for(m = 0; m < 6; m++){
payment = (amount / 10);
amount = amount - payment;
}
System.out.println(amount);
}
}

My outputs are always 1 more than the expected out put but I can't figure out where the error is. Please help.

Answer 1

Tommy Mensah

Your code will also work if you change the statement,

payment = (amount/10);

into

payment = (int) Math.ceil (amount * 0.1);

If you look closely at the example in Month 5:
Payment: 10% of 13122 = 1313

It's returning the smallest value that is greater than or equal to the argument.

So for rounding up purposes Java Math class has a method named ceil() which looks like this,

public static double ceil(double parameter)

Answer 2

Tommy Mensah Your statements inside the loop or say logic is what is wrong here .
Try this :

for( m=0;m<6;++m)
{
amount=amount*9/10;
}

Answer 3

Tommy Mensah

https://code.sololearn.com/cp6GXE4Rc84v/?ref=app

The reason why you get 10629 is because of Integer division. It ignores decimals (rounding down). Ultimately when you do a minus, you get an extra 1.

1: 20000 - 20000/10 = 18000
2: 18000 - 18000/10 = 16200
3: 16200 - 16200/10 = 14580
4: 14580 - 14580/10 = 13122
5: 13122 - 13122/10
= 13122 - 1312 (missing precision)
= 11810 (extra 1, expected 11809)
6: 11810 - 11810/10 = 10629

To bypass, you can do "amount = amount * 90 / 100".

Do not hard-code -1 or +1.

One good example will be 0. After 6 months, it will still be 0. By hard-coding -1, it results in -1 which is wrong.

Answer 4

Alphin K Sajan
Thanks Alphin, your solution worked. I'd appreciate some clarification on where my logic differed from yours. I still am unable to understand why introducing the payment amount in the calculation threw a wrong answer.

Answer 5

Tommy Mensah Hope you got the explanation from Minho 🇰🇷 .