debt_repayments.java

import java.text.DecimalFormat;

class Scratch {

    public static void main(String[] args) {
        try {
            int interestPercentage = Integer.parseInt(args[0]);
            int repaymentPercentage = Integer.parseInt(args[1]);

            double repaid = calculateTotalRepaid(interestPercentage, repaymentPercentage);

            DecimalFormat decimalFormat = new DecimalFormat("#.00");

            System.out.printf("Total amount repaid: $%s\n", decimalFormat.format(repaid));

        } catch (NumberFormatException | ArrayIndexOutOfBoundsException ex) {
            throw new RuntimeException("Invalid input!", ex);
        }
    }

    private static double calculateTotalRepaid(int interestPercentage, int repaymentPercentage) {
        int minRepayment = 50;
        double debt = 100d;

        double paid = 0;
        while (debt > 0d) {
            // add interest
            debt *= 1 + (interestPercentage / 100d);

            // perform payment
            double repayment = Math.min(
                    Math.max(
                            minRepayment,
                            debt * (repaymentPercentage / 100d)
                    ), debt);
            debt -= repayment;
            paid += repayment;
        }
        return paid;
    }

}