Java conversion code - why does the division not return the same result?

Question

Beginner question.
This might be more of a math problem, I sorted the code out, but I have no idea why the solution works. Please help explain:

As you may know, the formula for coversion from Celsius to Farenheit is

  F=C*9/5+32

Now, I am trying to write a simple Java code to do that conversion and I've defined the celsius and farenheit as double and also the final variable

  final double MAGIC_NUMBER=9/5;

then calculated the conversion

  farenheit=celsius*MAGIC_NUMBER+32;

The result was 24.0 celsius = 56.0 farenheit - which is not correct

I tried then defining the same thing in a different way:

  final double MAGIC_NUMBER=1.8;

And the result was 24.0 celsius = 75.2 farenheit - which is the correct one. Now, 1.8 is the same thing as 9/5. Why did the second assign work and not the first one?

Here is the whole code:

package farenheit;

import java.util.Scanner;
public class Farenheit {

public static void main(String[] args) {
   //declare variables
   double celsius;
   double farenheit;
   final double MAGIC_NUMBER=1.8;

   //prompt user to give me the temperature in celsius

   Scanner in=new Scanner(System.in);
   System.out.print("temperature in celsius= ");
   celsius=in.nextDouble();

   //calculate the conversion

   farenheit=celsius*MAGIC_NUMBER+32;

   //print out the result       
   System.out.printf("%.1f celsius = %.1f farenheit \n", celsius,      farenheit);
}  
 }

Thanks!