1
50.00
25.00
10.00
2
50.00
25.00
10.00
20.00

27.50
15.00

解题思路：
纯粹数学题，找规律:
An = (1/2)An-1 + (1/2)An+1 - Cn
An-1 = (2/3)An-2 + (1/3)An+1 - (2/3)Cn - (4/3)Cn-1
An-2 = (3/4)An-3 + (1/4)An+1 - (1/2)Cn - Cn-1 - (3/2)Cn-2
An-3 = (4/5)An-4 + (1/5)An+1 - (2/5)Cn - (4/5)Cn-1 - (6/5)Cn-2 - (8/5)Cn-3
......
（是不是有点感觉了呢）
接着:
A1 = (n/(n+1))A0 + (1/(n+1))An+1 - (2/(n+1))Cn - (4/(n+1))Cn-1 - ... -(2n/(n+1))C1
     = [ nA0 + An+1 - 2(Cn + 2Cn-1 + 3Cn-2 + ... + nC1) ]/(n+1)
源代码：
#include <stdio.h>
#include <stdlib.h> 
#define MaxSize 3001

int main()
{ 
  int i,n;
  double a1,a0,end;
  double c[MaxSize]; 
  while (scanf("%d",&n)!=EOF)
  { 
    scanf("%lf%lf",&a0,&end);
    for(i=0;i<n;i++)
      scanf("%lf",&c[i]);
    a1 = n* a0 + end ;
    for(i=0;i<n;i++)
      a1-=2*(i+1)*c[n-1-i]; 
    a1 =a1/(1 + n);
    printf ("%.2lf\n",a1);
  } 
  system("pause");
  return 0 ;
}