Answer to problem 21
package com.company;
import java.util.*;
import java.lang.*;

public class WhileLoopPractice1 {
    public static void main(String[] args)
    {
        Random rand = new Random();
        int secretNumber = rand.nextInt(7)+3;

        while(secretNumber != 5)
        {
            secretNumber = rand.nextInt(7)+3;
            System.out.println(secretNumber);
        }

    }
}

Answer to problem 22
package com.company;
import java.util.*;
import java.lang.*;

public class TwoRandomInts {
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        System.out.println("Type a number");
        int typedNumber = input.nextInt();
        int retypedNumber = input.nextInt();
        while(retypedNumber != 20) {
        System.out.println("Type a new number");
        retypedNumber = input.nextInt();
        if(retypedNumber > typedNumber && retypedNumber !=20){
            System.out.println(retypedNumber);
        }

    }
    }
}

Answer to problem 23
package com.company;
import java.util.*;
import java.lang.*;

public class WhileSums {
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        System.out.println("Type a number");
        int number1 = input.nextInt();
        System.out.println("Type a second number");
        int number2 = input.nextInt();
        while(number1 != -1 || number2 != -1) {
            System.out.println(number1+number2);
            System.out.println("Type a new number");
            number1 = input.nextInt();
            System.out.println("Type a second new number");
            number2 = input.nextInt();

        }
    }
}

Answer to problem 25
package com.company;
import java.util.*;
import java.lang.*;

public class SentenceConcatenater {
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);
        String sentence = "";
        String word = "";
        System.out.println("Type a sentence");
        sentence = input.nextLine();
        System.out.println("Type a second sentence");
        word = input.next();
        while(! word.equals("end")) {
            System.out.println(sentence+" "+word);
            System.out.println("Type a new sentence");
            sentence = input.nextLine();
            System.out.println("Type a second new sentence");
            word = input.next();

        }
    }
}