#include<bits/stdc++.h>
using namespace std;
const int mod=998244353;
const int maxn=3e5+5;
inline int read() {
	int x=0,f=1;
	char ch=getchar();
	while(ch<'0'||ch>'9') {if(ch=='-') f=-1;ch=getchar();}
	while(ch>='0'&&ch<='9') {x=(x<<1)+(x<<3)+(ch^48);ch=getchar();}
	return x*f;
}
typedef long long ll;
typedef long double lb;
int T,n,a[maxn];
int main() {
	T=read();
	while(T--) {
		n=read();
		int p=0,Min=2e9;
		for(int i=1;i<=n;++i) {
			a[i]=read();
			if(a[i]<Min) {
				Min=a[i];
				p=i;
			}
		}
		ll res=a[p]+a[p-1]+a[p+1];
		ll sum1=0,sum2=0;
		int now1=p-2,now2=n-p-1;
		for(int i=1;i<=now1;++i) sum1+=a[i];
		for(int i=p+2;i<=n;++i) sum2+=a[i];
		lb ans=(lb)(sum1+sum2+res)/(lb)n;
		ll tmp=0;
		for(int i=p-2;i;--i) {
			tmp+=a[i];
			ans=max(ans,(lb)(tmp+res)/(lb)(p+3-i));
			ans=max(ans,(lb)(tmp+res+sum2)/(lb)(n-i+1));
		}
		tmp=0;
		for(int i=p+2;i<=n;++i) {
			tmp+=a[i];
			ans=max(ans,(lb)(tmp+res)/(lb)(i-p+2));
			ans=max(ans,(lb)(tmp+res+sum1)/(lb)i);
		}
		ans=max(ans,(lb)res/3.0);
		printf("%.15Lf\n",ans);
	}
	return 0;
}