#include <cstdio>

#include <cstring>

#include <iostream>

#include <algorithm>

using namespace std;

#define F(i,j,k) for (int i=j;i<=k;++i)

#define D(i,j,k) for (int i=j;i>=k;--i)

#define ll long long

#define maxn 50005

int t,n,k;

ll a[maxn],sum[maxn],sumfac[maxn];

int main()

{

    scanf("%d",&t);

    while (t--)

    {

        scanf("%d%d",&n,&k);

        F(i,1,n) scanf("%lld",&a[i]);

        if (k>=n-1){printf("0\n");continue;}

        sort(a+1,a+n+1);

        sum[0]=sumfac[0]=0;

        F(i,1,n) sum[i]=sum[i-1]+a[i];

        F(i,1,n) sumfac[i]=sumfac[i-1]+a[i]*a[i];

        double ans=1e18;

        k=n-k;

        F(i,1,n-k+1)

        {ans=min(ans,(double)sumfac[i+k-1]-sumfac[i-1]+(double)(sum[i+k-1]-sum[i-1])*(sum[i+k-1]-sum[i-1])/k-(double)2*(sum[i+k-1]-sum[i-1])*(sum[i+k-1]-sum[i-1])/k);}

        printf("%f\n",ans);

    }

}