#include <cstdio>

#include <iostream>

#include <cmath>

#include <algorithm>

#include <cstdlib>

#include <cstring>

#include <queue>

#define ll long long

using namespace std;

const int maxn = ;

int main(){

    int t,n,k;

    ll a[maxn];

    scanf("%d",&t);

    while(t--){

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

        for(int i=;i<=n;i++) scanf("%lld",&a[i]);

        if(n==k){

            printf("0.000000000\n");

            continue;

        }

        sort(a+,a++n);

        ll sum=,tot=;

        for(int i=;i<=n-k;i++){

            sum+=a[i];

            tot+=a[i]*a[i];

        }

        double ave=(sum*1.0)/(n-k);

        double ans=ave*ave*(n-k)+tot-*ave*sum;

        for(int i=;i<=k+;i++){

            sum=sum-a[i-]+a[n-k+i-];

            tot=tot-a[i-]*a[i-]+a[n-k+i-]*a[n-k+i-];

            ave=(sum*1.0)/(n-k);

            double t=ave*ave*(n-k)+tot-*ave*sum;

            ans=min(t,ans);

        }

        printf("%.9lf\n",ans);

    }

    return ;

}