REVIEW:

a) 

public static void main(String []args) {
        //declaring and initializing variables
        int fact = 1;
        int i = 1;

        //creating object of Scanner class
        Scanner sc = new Scanner(System.in);

        //accepting a number from the user
        System.out.print("Enter a number whose factorial is to be found: ");
        int num = sc.nextInt();

        //counting the factorial using while loop
        while( i <= num ) {
            fact = fact * i;
            i++; //increment i by 1
        }

        //printing the result
        System.out.println("\nFactorial of " + num + " is: " + fact);
    }

b) 

import java.util.Scanner;

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

        // Step 1: Prompt the user
        System.out.print("Enter an integer: ");
        int num = input.nextInt();

        // Step 2: Create variables
        int reverseNum = 0; // to hold reversed number
        int rem = 0;        // to hold remainders

        // Step 3: Loop until num becomes 0
        while (num != 0) {
            // get remainder (last digit)
            rem = num % 10;

            // shift digits in reverseNum to the left
            reverseNum = reverseNum * 10 + rem;

            // remove last digit from num
            num = num / 10;
        }

        // Step 4: Output the result
        System.out.println("Reversed number: " + reverseNum);

        input.close();
    }
}

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1)

a. 

for(int i = 1; i <= 20; i++){
   if(i % 2 == 0){
     System.out.println(i);
   }
}

OR

for(int i = 2; i <= 20; i+=2){
   System.out.println(i);
}

b. 

for(int i = 30; i <= 50; i++) {
   if(i % 2 != 0) {
     System.out.println(i);
   }
}

OR 

for(int i = 31; i <= 50; i+=2) {
   System.out.println(i);
}


c. 

for(int i = 10; i > 0; i--) {
   System.out.println(i);
}

d. 

int sum = 0;
for(int i = 1; i <= 15; i++) { //runs 15 times
   sum += i * 5;
}
System.out.println(sum);