Help with one of my first progys

Question

the fallowing code is for an intro to comp sci class I'm taking. I'm very new to java and I'm just having a small issue with this code
when it spits out the output for the final letter grade variable:sLettergrade it is many times incorrect or just spits out a blank but it's also sometimes right.
after quite some time trying to figure it out I have resorted to this any help would be fantastic!
package studentgrades;
import java.io.*; 
//@author Preston Taylor
public class Main {
//@param args the command line arguments
    public static void main(String[] args) {
        //this block sets up the program for user input
        InputStreamReader charReader = new
            InputStreamReader(System.in);
        BufferedReader keyboard = new
            BufferedReader(charReader);
        try{
            //variable declaration
            String sInput= ""; /*only used for input that requires prasing.
                                *must be parsed out of and decalred to another varible
                                *immediately so it can be used at the next input*/
            String sLoop=""; //variable used to continue loop
            String sFirstname="";
            String sLastname="";
            String sLettergrade="";
            int iStudentnumber=0;
            double dHomework=0;
            double dQuiz=0;
            double dMidterm=0;
            double dFinalscore=0;
            double dGradepercent=0; //final grade percentage after calulations
            //the next do statement is the main loop of the program
            //that the program comes back to if the user decides to continue
            do{
                //inquiry to the user
                System.out.println("What is the Student number?");
                    sInput=keyboard.readLine();
                    iStudentnumber=Integer.parseInt(sInput);
                System.out.println("Student first name?");
                    sFirstname=keyboard.readLine();
                System.out.println("Student last name?");
                    sLastname=keyboard.readLine();
                System.out.println("What is the homework average percent?");
                    sInput=keyboard.readLine();
                    dHomework=Double.parseDouble(sInput);
                System.out.println("What is the Quiz average percent?");
                    sInput=keyboard.readLine();
                    dQuiz=Double.parseDouble (sInput);
                System.out.println("What is the Midterm score percent?");
                    sInput=keyboard.readLine();
                    dMidterm=Double.parseDouble(sInput);
                System.out.println("What is the Final test score percent?");
                    sInput=keyboard.readLine();
                    dFinalscore=Double.parseDouble(sInput);
               //equations to figure final grade
               dHomework=dHomework*.4;
               dQuiz=dQuiz*.2;
               dMidterm=dMidterm*.2;
               dFinalscore=dFinalscore*.2;
               dGradepercent=dHomework+dQuiz+dMidterm+dFinalscore;
               //the fallowing if statements assign a letter grade to the percentage
               if (dGradepercent >= 90)
                   sLettergrade="A";
               if (dGradepercent < 90 && dFinalscore >=80)
                   sLettergrade="B";
               if (dGradepercent < 80 && dFinalscore >=70 )
                   sLettergrade="C";
               if (dGradepercent < 70 && dFinalscore >= 60)
                   sLettergrade="D";
               if (dGradepercent < 60)
                   sLettergrade="FAILURE";
               //the fallowing is readout to the user
               System.out.println(sLastname + ", " + sFirstname + " with a student id of " + iStudentnumber);
               System.out.println("Homework: " + dHomework);
               System.out.println("Quizzes: " + dQuiz);
               System.out.println("Midterm: " + dMidterm);
               System.out.println("Final Test " + dFinalscore);
               System.out.println(" ");
               System.out.println("Final average: " + "%" + dGradepercent + " Grade: " + sLettergrade);
                do{ //the fallowing loop covers incompetent user handling
                    System.out.println("would you like to enter another student? y or n");
                    sLoop= keyboard.readLine();
                    if (!((sLoop.equals ("y")) || (sLoop.equals ("Y")) || (sLoop.equals ("n")) || (sLoop.equals ("N"))))
                        System.out.println("ERROR: you typed something incorrect try again");
                //the below while statement loops back to the do statement above if the user is retarded or has fat fingers
                }while (!((sLoop.equals ("y")) || (sLoop.equals ("Y")) || (sLoop.equals ("n")) || (sLoop.equals ("N"))));
            //the next while statement handles exiting and looping the program
            }while ((sLoop.equals ("y")) || (sLoop.equals ("Y")));
        catch (IOException e){
            System.out.print("error "+ e.getMessage()); //error handling
}thanks, Preston

Answer 1

if you're testing a range, shouldn't the variables be the same?
if (dGradepercent < 90 && dFinalscore >=80)
if (dGradepercent < 90 && dGradepercent >=80)
                                ^^^