#include<cstring>#include<cstdio>#include<algorithm>#include<cstdlib>#define MAXN 10010using namespace std;struct Graph{ int next,vex,dis;};Graph g[MAXN<<1];int n,first[MAXN],ch[MAXN],a[MAXN],dis[MAXN],s[MAXN],pre[MAXN];bool visited[MAXN];void AddEdge(int v,int w,int d,int i){ g[i].dis=d; g[i].vex=w; g[i].next=first[v]; first[v]=i;}void DFS(int v){ int i,w; visited[v]=true; for(i=first[v];i!=-1;i=g[i].next) { w=g[i].vex; if(!visited[w]) { ch[v]++; pre[w]=v; dis[w]=g[i].dis; DFS(w); } }}int main(){ int t,i,j,k,v,w,d; double ans; scanf("%d",&t); while(t--) { scanf("%d",&n); memset(visited,false,sizeof(visited)); memset(first,-1,sizeof(first)); memset(ch,0,sizeof(ch)); memset(a,0,sizeof(a)); for(i=j=0;j+1<n;j++) { scanf("%d%d%d",&v,&w,&d); AddEdge(v,w,d,i);i++; AddEdge(w,v,d,i);i++; } DFS(0); pre[0]=-1; for(i=k=0,ans=0;i<n;i++) if(!ch[i]) s[k++]=i; for(i=0;i<k;i++) { v=s[i]; w=pre[v]; if(w==-1) break; a[v]++; ans+=1.0*dis[v]*a[v]*(n-a[v]); a[w]+=a[v]; if(!(--ch[w])) s[k++]=w; } printf("%lfn",ans*2/(n*(n-1))); } return 0;}
