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);
    }
}

9.10