#include<cstdio>
#include<vector>
using namespace std;

 
typedef vector<pair<int,int> >::iterator it;
 

#define MaxN 110000

#define ll long double
 

#define ld long double
 

int N;
int T[MaxN],Fii[MaxN],viz[MaxN];
vector<pair<int,int> > A[MaxN];

void citire(void)
{
    int a,b,c;

    scanf("%d",&N);
    for(int i=1;i<N;i++)
    {

        A[b].push_back(make_pair(a,c));
    }
}

inline void DF(int nod)
{
    viz[nod] = 1;
    Fii[nod] = 1;

    for(int i=0;i<A[nod].size();i++)
        if(!viz[A[nod][i].first])

    for(it i=A[nod].begin();i<A[nod].begin();i++)
        if(!viz[i->first])

        {

            DF(A[nod][i].first);
            T[A[nod][i].first] = nod;
            Fii[nod] += Fii[A[nod][i].first];

            DF(i->first);
            T[i->first] = nod;
            Fii[nod] += Fii[i->first];

        }
}

inline double suma(void)
{

    ll sum = 0;
 

    ld sum = 0;
 

    for(int i=0;i<=N;i++)

        for(int j=0;j<A[i].size();j++)
            if(A[i][j].first > i)

        for(it j=A[i].begin();j<A[i].end();j++)
            if(j->first > i)

            {

                if(T[i] != A[i][j].first)
                    sum += (ll)A[i][j].second*Fii[A[i][j].first]*(N-Fii[A[i][j].first]);

                if(T[i] != j->first)
                    sum += (ld)j->second*Fii[j->first]*(N-Fii[j->first]);

                else

                    sum += (ll)A[i][j].second*Fii[i]*(N-Fii[i]);

                    sum += (ld)j->second*Fii[i]*(N-Fii[i]);

            }

 
    return sum/((ll)N*(N-1)/2);

 
    return sum/((ld)N*(N-1)/2);

}

inline void sterge(void)
{
    for(int i=0;i<N;i++)

        A[i].clear(), Fii[i] = T[i] = viz[i] = 0;

    {
        A[i].clear();
        Fii[i] = T[i] = viz[i] = 0;
    }

}

int main()
{

    //freopen("test.txt","r",stdin);
    int T;
    scanf("%d",&T);
 
    for(int i=1;i<=T;i++)

    int nrTeste;
    scanf("%d",&nrTeste);
 
    for(int i=1;i<=nrTeste;i++)

    {
        citire();
        DF(0);

        printf("%lf\n",suma());
        sterge();
    }

    return 0;
}
==