sum/4.0为什么会是26.25呢？

public static void main(String[] args) {
  int age1=24; int age2=18; int age3=36; int age4=27;
  int sum = age1 + age2 + age3 + age4;
  double avg = sum/4.0;  
  System.out.println("年龄总和："+sum);
  System.out.println("平均年龄："+avg);
  }