#include <cmath>
#include <cstdio>
#include <algorithm>

#define MAX_N 100000

double solve(const int V[], int N, int K)
{
    if (K == 1)
    {
        return V[N-1];
    }
    double weight[MAX_N];
    double totalWeight = 0;
    for (int i = 0; i < N; i++)
    {
        weight[i] = pow(V[i], -1./(K-1));
        totalWeight += weight[i];
    }
    int zeros = 0;
    double res = 0;
    for (int i = 0; i < N; i++)
    {
        double q = (N-1-zeros)*weight[i]/(totalWeight);
        if (q > 1)
        {
            zeros++;
            totalWeight -= weight[i];
        }
        else
        {
            res += V[i] * (1-pow(q, K));
        }
    }
    return res / K;
}

int main()
{
    int T;
    scanf("%d", &T);
    for (int tt = 0; tt < T; tt++)
    {
        int N, K;
        scanf("%d%d", &N, &K);
        int V[MAX_N];
        for (int i = 0; i < N; i++)
            scanf("%d", V+i);
        std::sort(V, V+N);
        double res = solve(V, N, K);
        printf("%.12f\n", res);
    }
}