How do we use a variable from one method to another for eg im trying divide one variable by another

I'm trying to divide variables from pointsearned and creditsearned method in the pointsaverage method but it gives "Your grade point average isNaN" when i run it , how do i fix this ?(I'm a beginner)

public class JavaApplication40 {
static Scanner keyboard = new Scanner(System.in);
public static void main(String[] args) {
double credits = 0;
double Points = 0;
double average = 0;
IDnumber();
CreditsEarned(credits);
PointsEarned(Points);
System.out.println("Your grade point average is" +  PointAverag(average, Points, credits));
}
public static void IDnumber(){
String docNuMBER; 
System.out.println("Enter your student ID number ");
docNuMBER = keyboard.nextLine();
}
public static double CreditsEarned( double credits){
double NumCreditsEarned;
System.out.println("Enter your Credit hours earned");
NumCreditsEarned = keyboard.nextDouble(); 
return NumCreditsEarned;
}
public static double PointsEarned(double points){
double NumberOpoints;
System.out.println("Enter your credit points");
NumberOpoints = keyboard.nextDouble();
return NumberOpoints;
}
public static double PointAverag(double grade , double NumberOpoints ,
double NumCreditsEarned) {
double average ;
average =   NumberOpoints/NumberOpoints;
return average ;

Here's what's happening in your program:

You set 'credits' and 'points' to 0.
These two variables have not been modified when you get to pass them to 'pointAverag'

System.out.println("Your grade point average is" +  PointAverag(average, Points, credits));

this line, literally, does this:

System.out.println("Your grade point average is" +  PointAverag(0, 0, 0));

And eventually leads to:

average = 0/0

<strong>in 'PointAverag' which is NAN when stored in a double.</strong>

Watch out for this line:

average =   NumberOpoints/NumberOpoints;

it has logical mistake in it. It will always store either 1 or NAN.

As mentionned in the comments, you need to update those variables, 'credits' and 'points', by storing the returned value of your methods 'PointsEarned' and 'CreditsEarned' in them:

CreditsEarned(credits);
PointsEarned(Points);

Becomes

credits = CreditsEarned(credits);
points = PointsEarned(Points);

Hope this helps.

Write:

System.out.println("Your grade point average is" +  PointAverag(IDnumber(), PointsEarned(Points), CreditsEarned(credits)));

instead.

If you don't use a returned value, it gets discarded.