#include<cstdio>

 #include<iostream>

 #include<algorithm>

 #include<cstring>

 #include<cmath>

 #include<queue>

 #include<map>

 using namespace std;

 #define MOD 1000000007

 const int INF=0x3f3f3f3f;

 const double eps=1e-;

 typedef long long ll;

 #define cl(a) memset(a,0,sizeof(a))

 #define ts printf("*****\n");

 const int MAXN=;

 int n,m,tt;

 int a[MAXN];

 int main()

 {

     int i,j,k,ca=;

     #ifndef ONLINE_JUDGE

     freopen("1.in","r",stdin);

     #endif

     scanf("%d",&tt);

     while(tt--)

     {

         cin>>n;

         int w,sum=;

         printf("Case %d: ",ca++);

         for(i=;i<n;i++)

         {

             int a;

             scanf("%d",&a);

             if(i==)    w=a;

             sum+=a;

         }

         printf("%.6lf\n",(double)w/sum);

     }

 }