I understand that the theory of binary numbers, so operation of double numbers is not precise. However, in java, I have no idea why "(double)65 / 100" is 0.65, which is completely correct in decimal number, other than 0.6500000000004.

double a = 5;
double b = 4.35;
int c = 65;
int d = 100;
System.out.println(a -  b); // 0.6500000000000004
System.out.println((double) c /  d); // 0.65