1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 #include <cmath>
 6 #include <string>
 7 #include <map>
 8 #include <stack>
 9 #include <vector>
10 #include <set>
11 #include <queue>
12 #pragma comment (linker,"/STACK:102400000,102400000")
13 #define maxn 50050
14 #define MAXN 2005
15 #define mod 1000000009
16 #define INF 0x3f3f3f3f
17 #define pi acos(-1.0)
18 #define eps 1e-6
19 typedef long long ll;
20 using namespace std;
21 
22 double a[maxn];
23 
24 int main()
25 {
26     int n,k,cas;
27     double t,sum1,sum2;
28     scanf("%d",&cas);
29     while (cas--)
30     {
31         scanf("%d%d",&n,&k);
32         sum1=0.0;
33         sum2=0.0;
34         for (int i=1;i<=n;i++)
35             scanf("%lf",&a[i]);
36         if (n==1||n==k||k==(n-1))
37         {
38             printf("0.00000000000\n");
39             continue;
40         }
41         sort(a+1,a+n+1);
42         for (int i=1;i<=n-k;i++)
43         {
44             sum1+=a[i];
45             sum2+=a[i]*a[i];
46         }
47         double ans=(n-k)*sum2-sum1*sum1;
48         for (int i=1;i<=k;i++)
49         {
50             sum1=sum1+a[n-k+i]-a[i];
51             sum2=sum2+a[n-k+i]*a[n-k+i]-a[i]*a[i];
52             double temp=(n-k)*sum2-sum1*sum1;
53             if (temp<ans)
54                 ans=temp;
55         }
56         printf("%.11f\n",(double)ans/(double)(n-k));
57     }
58     return 0;
59 }