1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <string>
 5 #include <algorithm>
 6 #include <cmath>
 7 #include <vector>
 8 #include <queue>
 9 #include <map>
10 #include <stack>
11 #include <set>
12 using namespace std;
13 typedef long long LL;
14 typedef unsigned long long uLL;
15 #define ms(a, b) memset(a, b, sizeof(a))
16 #define pb push_back
17 #define mp make_pair
18 #define eps 0.0000000001
19 #define IOS ios::sync_with_stdio(0);cin.tie(0);
20 const LL INF = 0x3f3f3f3f3f3f3f3f;
21 const int inf = 0x3f3f3f3f;
22 const int mod = 1e9+7;
23 const int maxn = 50000+10;
24 double a[maxn];
25 double sum[maxn];
26 double sum_pow[maxn];
27 void solve()
28 {
29     ms(sum, 0);ms(sum_pow, 0);
30     int n, k;scanf("%d%d", &n, &k);
31     for(int i = 1;i<=n;i++)  scanf("%lf", &a[i]);
32     sort(a+1, a+1+n);
33     for(int i = 1;i<=n;i++){
34         sum[i] = sum[i-1] + a[i];
35         sum_pow[i] = sum_pow[i-1] + a[i]*a[i];
36     }
37     if(n-k<=1){
38         printf("0.0000000000\n");return;
39     }
40     double ans = (double)INF;
41     for(int i = n-k;i<=n;i++){
42         double A = (double)(n-k);
43         double B = -2.0*(sum[i]-sum[i-(n-k)]);
44         double C = sum_pow[i] - sum_pow[i-(n-k)];
45         double x = -B/(2.0*A);
46 //        printf("%f %f %f %f\n", A, B, C, x);
47 //        printf("%f\n", A*x*x + B*x + C);
48 
49         ans = min(ans, A*x*x + B*x + C);
50     }
51     printf("%.10f\n", ans);
52     return;
53 }
54 int main() {
55 #ifdef LOCAL
56     freopen("input.txt", "r", stdin);
57 //        freopen("output.txt", "w", stdout);
58 #endif
59 //    IOS
60     int t;scanf("%d", &t);
61     while(t--)
62         solve();
63     return 0;
64 }