uva 10014

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;

int main()
{
    int t,n;
    double af,al,c,sum;
    cin>>t;
    while (t--)
    {
        cin>>n>>af>>al;
        sum = 0 ;
        for (int i = 0 ; i < n ; i++)
        {
            cin>>c;
            sum += (n-i) * c;
        }
        printf("%0.2lf\n",(n*af + al - 2 * sum)/(n+1));
        if (t)
            printf("\n");
    }
    return 0;
}