#include <bits/stdc++.h>
using namespace std;
int main()
{
double a0,an,a1,a,b,t,tc,n;
double c[3002];
int i;
cin>>t;
while(t--)
{
b=0;
cin>>n;
cin>>a0>>an;
if(n==0) printf("%0.2lf\n",an);
else{
for( i=0;i<n;i++)
{
cin>>c[i];
b+=((n-i)*c[i])*2;
}
a=((n*a0)+an);
a1=(a-b)/(n+1);
printf("%0.2lf\n",a1);
}
if(t) printf("\n");
}
return 0;
}
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