#include <bits/stdc++.h>   using namespace std;   template <typename T>   void smax(T &a, T b) {     if (a < b) a = b;   }   const double EPS = 1e-9;   vector<pair<pair<int, int>, int> > adj[100000 + 10];   long long totSum;   pair<pair<int, int>, int> edges[100000 + 10];   int belows[100000 + 10];   int n;   pair<long long, int> f(int u, int jad) {     long long sum = 0;     int cnts = 0;     for (int i = 0; i < ((int)(adj[u]).size()); ++i) {       int v = adj[u][i].first.first;       int cost = adj[u][i].first.second;       int edge = adj[u][i].second;       if (v == jad) {         continue;       }       pair<long long, int> temp = f(v, u);       int cnt = temp.second;       long long belowSum = temp.first + (long long)cost * cnt;       belows[edge] = cnt;       totSum += cnt * sum;       totSum += cnts * belowSum;       sum += belowSum;       cnts += cnt;     }     cnts++;     totSum += sum;     return make_pair(sum, cnts);   }   inline long long getDollarBabe(long long temp) { return temp * (n - temp); }   int main(int argc, char const *argv[]) {     ios_base::sync_with_stdio(false);     cin.tie(0);     cin >> n;     for (int i = 0; i < n - 1; ++i) {       int u, v, len;       cin >> u >> v >> len;       if (u > v) {         swap(u, v);       }       u--;       v--;       adj[u].push_back(make_pair(make_pair(v, len), i));       adj[v].push_back(make_pair(make_pair(u, len), i));       edges[i] = make_pair(make_pair(u, v), len);     }     totSum = 0;     f(0, -1);     int q;     cin >> q;     while (q--) {       int r, w;       cin >> r >> w;       r--;       int temp = belows[r];       totSum -= (edges[r].second - w) * getDollarBabe(temp);       edges[r].second = w;       cout << fixed << setprecision(8)            << (double)totSum * 6 / ((long long)(n) * (n - 1)) << endl;     }     return 0;   }   