#include <bits/stdc++.h>
using namespace std;
template <class T>
T gcd(T a, T b) {
  T r;
  while (b != 0) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
template <class T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
template <class T>
int getbit(T s, int i) {
  return (s >> i) & 1;
}
template <class T>
T onbit(T s, int i) {
  return s | (T(1) << i);
}
template <class T>
T offbit(T s, int i) {
  return s & (~(T(1) << i));
}
const double PI = 2 * acos(0.0);
const double eps = 1e-9;
const int infi = 1e9;
const long long Linfi = (long long)2e18;
const long long MOD = 1000000007;
const int c1 = 11;
const int c2 = 13;
struct road {
  int st, en, w;
  road() {}
  road(int _st, int _en, int _w) {
    st = _st;
    en = _en, w = _w;
  }
};
int n, u, v, c, m;
vector<pair<long long, int> > adj[100005];
int F[100005];
int xet[100005];
road E[100005];
void DFS(int u) {
  xet[u] = 1;
  F[u] = 1;
  for (int i = 0; i < adj[u].size(); i++) {
    int v = adj[u][i].second;
    if (xet[v] == 0) {
      DFS(v);
      F[u] = F[u] + F[v];
    }
  }
}
void solve() {
  long long ans = 0;
  DFS(1);
  for (int u = 1; u <= n; u++) {
    for (int i = 0; i < adj[u].size(); i++) {
      int v = adj[u][i].second;
      long long w = adj[u][i].first;
      long long tmp = min(F[u], F[v]);
      ans += tmp * (n - tmp) * w;
    }
  }
  ans /= 2;
  cin >> m;
  while (m--) {
    int x, nC;
    cin >> x >> nC;
    int u = E[x].st;
    int v = E[x].en;
    int c = E[x].w;
    E[x].w = nC;
    long long delta = c - nC;
    long long cnt = min(F[u], F[v]);
    ans = ans - cnt * (n - cnt) * delta;
    cout << fixed << setprecision(6);
    cout << 6.0 * ans / (1.0 * (n - 1) * (n)) << endl;
  }
}
int main() {
  ios::sync_with_stdio(false);
  cin >> n;
  for (int i = 1; i <= n - 1; i++) {
    cin >> u >> v >> c;
    E[i] = road(u, v, c);
    adj[u].push_back(pair<long long, int>(c, v));
    adj[v].push_back(pair<long long, int>(c, u));
  }
  solve();
  return 0;
}
