#include<iostream>
#include<cstdio>
#include<cassert>
#include<algorithm>
using namespace std;

const int mN=300005;
int n,a[mN]; 
//long long pre[mN];
int main()
{
	//freopen("","r",stdin);//freopen("","w",stdout);
	int tsk;
	scanf("%d",&tsk);
	while(tsk--){
		scanf("%d",&n);
//		pre[0]=0;
		for(int i=1;i<=n;++i){
			scanf("%d",a+i);
//			pre[i]=pre[i-1]+a[i];
		}
		int v=0;
		for(int i=1;i<=n;++i)
			if(i>1&&i<n&&a[i]<a[i-1]&&a[i]<a[i+1])
				v=i;
		assert(v!=0);
		double l=0,m=0,r=0;
		m=a[v-1]+a[v]+a[v+1];
		for(int i=1;i<v-1;++i) l+=a[i];
		for(int i=v+2;i<=n;++i) r+=a[i];
		printf("%.12lf\n",max(max((l+m)/(v+1),(m+r)/(n-v+2)),(l+m+r)/n));
//		printf("%.12lf\n",max(max((double)1.0*pre[v+1]/(v+1),
//								(double)1.0*(pre[n]-pre[v-2])/(n-v+2)),(double)1.0*pre[n]/n));
	}
	//fclose(stdin);//fclose(stdout);
	return 0;
}