Java lesson 20 can't pass test cases

Question

My code
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

for (int i = 0; i < 3; i++){
int payment = (amount / 100) * 10;
amount = amount - payment;

}
System.out.println(amount);
}
}

And it gives me the same output as the test case. But says that there is a bug. Can somebody help ?

Answer 1

It's an integer precision problem. This works:

for (int i = 0; i < 3; i++){
double payment = (amount / 100.0) * 10;
amount = amount - (int) payment;
}
System.out.println(amount);

And this solution as said Jay Matthews

for (int i = 0; i < 3; i++){
int payment = amount/10;
amount = amount - payment;
}
System.out.println(amount);

Answer 2

Another approach:

Every month, if you pay 10% it remains the 90%
First month: remainingAmount1 = amount * 0.9
Second month: remainingAmount2 = remainingAmount1 * 0.9 = amount * 0.9 * 0.9
And so on

You can solve this using a loop or using Math.pow

Answer 3

Mathematics is an exact science and the approach to it must be strictly in accordance with its laws. ☺️
You have been given a certain amount, for example $2000.
You need to subtract 10% from it, that is, 10% of 100%, that is, $2000 is 100%.
Agree, it will be strange 100% / 100% ☺️
To find 10% of an integer, you need to multiply the integer by a tenth of the integer, that is, 10/100, as a result we get:
payment = amount * 10/100;
10/100 can be reduced by 10:
payment = amount * 1/10,
which corresponds to:
payment = amount / 10;
As a result of the calculation formula
payment = amount * 10/100;
and
payment = amount / 10;
are correct, as created according to mathematical rules.

2000 / 10 = 200
2000 - 200 = 1800

1800 / 10 = 180
1800 - 180 = 1620

1620 / 10 = 162
1620 - 162 = 1458