3-1
import java.util.Scanner;
public class Hua01 { public static void main(String[] args) { int number1=(int)(System.currentTimeMillis()%10); int number2=(int)(System.currentTimeMillis()/7%10); Scanner input=new Scanner(System.in); System.out.print( "What is "+number1+"+"+number2+"?"); int answer = input.nextInt(); System.out.println( number1+"+"+number2+"="+answer+" is "+(number1+number2==answer)); } }

3-2
import java.util.Scanner;
public class Hua02 { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.println("Enter an integer:"); int number = input.nextInt(); if (number % 5 == 0) System.out.println("HiFive"); if(number % 2 == 0) System.out.println("HiEven"); } }

3-3
import java.util.Scanner;
public class Hua03 { public static void main(String[] args) { int number1 = (int)(Math.random() * 10); int number2 = (int)(Math.random() * 10); if (number1 < number2) { int temp = number1; number1 = number2; number2 = temp; } System.out.print ("What is " + number1 + "-" + number2 + "?"); Scanner input = new Scanner(System.in); int answer = input.nextInt(); if (number1 - number2 == answer) System.out.println("You are correct!"); else{ System.out.println("Your answer is wrong."); System.out.println(number1 + "-" + number2 + "should be " + (number1-number2)); } } }

3-4
import java.util.Scanner;

public class Hua04  
{
    public static void main(String[] args) 
    {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter weight in kilograms:");
        double weight = input.nextDouble();

        System.out.print("Enter height in meters:");
        double height = input.nextDouble();

        double bmi = weight/(height * height);

        System.out.println("BMI is " + bmi);
        if (bmi < 18.5)
            System.out.println("Underweight");
        else if (bmi < 25)
            System.out.println("Normal");
        else if (bmi < 30)
            System.out.println("Overweight");
        else
            System.out.println("Obese");
    }
}

3-6
import java.util.Scanner;

public class Hua06
{
    public static void main(String[] args) 
    {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter an integer:");
        int number = input.nextInt();
        if (number % 2 == 0 && number % 3 ==0)
            System.out.println(number + " is divisible by 2 and 3.");
        if (number % 2 == 0 || number % 3 ==0)
            System.out.println(number + " is divisible by 2 or 3.");
        if (number % 2 == 0 ^ number % 3 ==0)
            System.out.println(number + " is divisible by 2 or 3, but not both.");
    }
}

3-7
import java.util.Scanner;

public class Hua07 
{
    public static void main(String[] args) 
    {
        Scanner input = new Scanner(System.in);

        System.out.print("Enter a year:");
        int year = input.nextInt();
        boolean isLeapYear = (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
            System.out.println(year + " is a leap year?" + isLeapYear);
    }
}