Pq a conta esta errada?

public class Simple1{
	public static void main(String arg[]){
		int a;
		double b, c;
		
		a=3;
		b=5.2;
		c=a+b;
		
		System.out.println("-------");
		
		System.out.println("a= "+a);
		System.out.println("b= "+b);
		System.out.println("c= "+c);
		
		System.out.println("-------");
		
		System.out.println("c= "+c+" - "+b);
		c=c-b;
		System.out.println("c= "+c);
		
		System.out.println("-------");
		
		System.out.println("???????");
	}
}

a=3;
b=5.2;
c=8.2
-------
c= 8.2 - 5.2
c= 2.999999999999999	
-------
???????