Homework - Programming

package javaapplication50;

import java.util.Scanner;

public class JavaApplication50 {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter grade or -1 to quit:");
        int number = 0;
        int sum = 0;
        int students = 1;
        double average = 0;
        int freq50 = 0;
        int freq50to60 = 0;
        int freq60to70 = 0;
        int freq70to80 = 0;
        int freq80to90 = 0;
        int freq90to100 = 0;
        while (number != -1) {
            number = scanner.nextInt();
            if (number < 50 && number >= 0) {
                freq50++;
            } else if (number >= 50 && number < 60) {
                freq50to60++;
            } else if (number >= 60 && number < 70) {
                freq60to70++;
            } else if (number >= 70 && number < 80) {
                freq70to80++;
            } else if (number >= 80 && number < 90) {
                freq80to90++;
            } else if (number >= 90 && number <= 100) {
                freq90to100++;
            }
            if (number != -1) {
                sum = sum + number;
                students++;
            }
        }
        students--;
        average = sum / students;
        System.out.println("Marks\t\tFrequency");
        System.out.println("below 50\t" + freq50);
        System.out.println("50-60\t\t" + freq50to60);
        System.out.println("60-70\t\t" + freq60to70);
        System.out.println("70-80\t\t" + freq70to80);
        System.out.println("80-90\t\t" + freq80to90);
        System.out.println("90-100\t\t" + freq90to100);
        System.out.println("****************************");
        System.out.println("Class Average is " + average);
    }
}