#include <bits/stdc++.h>
using namespace std;
const long double pi = 3.1415926535897932384626433832795l;
template <typename T>
inline auto sqr(T x) -> decltype(x * x) {
  return x * x;
}
template <typename T>
inline T abs(T x) {
  return x > T() ? x : -x;
}
template <typename T1, typename T2>
inline bool umx(T1& a, T2 b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename T1, typename T2>
inline bool umn(T1& a, T2 b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
const int N = 100100;
struct Input {
  int n;
  vector<pair<int, int> > a[N];
  int len[N];
  int num[N], w[N];
  int q;
  bool read() {
    if (scanf("%d", &n) != 1) return 0;
    for (int i = 0; i < int(n - 1); ++i) {
      int u, v;
      scanf("%d %d %d", &u, &v, &len[i]);
      u--, v--;
      a[u].push_back(make_pair(v, i));
      a[v].push_back(make_pair(u, i));
    }
    cin >> q;
    for (int i = 0; i < int(q); ++i) {
      scanf("%d %d", &num[i], &w[i]);
      num[i]--;
    }
    return 1;
  }
  void init(const Input& input) { *this = input; }
};
struct Data : Input {
  long double ans[N];
  void write() {
    for (int i = 0; i < int(q); ++i) {
      printf("%0.15lf\n", (double)ans[i]);
    }
  }
  virtual void solve() {}
  virtual void clear() { *this = Data(); }
};
struct Solution : Data {
  int sz[N];
  int kol[N];
  bool use[N];
  int dfs(int v, int idx = -1) {
    use[v] = 1;
    sz[v] = 1;
    for (int i = 0; i < int(a[v].size()); ++i) {
      int to = a[v][i].first;
      if (use[to]) continue;
      sz[v] += dfs(to, a[v][i].second);
    }
    if (idx >= 0) kol[idx] = sz[v];
    return sz[v];
  }
  inline long double c(int a, int b) {
    if (a < b) return 0;
    if (b == 0) return 1;
    if (b == 1) return a;
    if (b == 2) {
      return (long double)a * (a - 1) / 2.0;
    }
    return (long double)a * (a - 1) * (a - 2) / 6.0;
  }
  inline long double get(int i) {
    return 2.0 * (long double)kol[i] * c((n - kol[i]), 2) +
           2.0 * (long double)(n - kol[i]) * c(kol[i], 2);
  }
  void solve() {
    dfs(0);
    long double res = 0;
    for (int i = 0; i < int(n - 1); ++i) {
      res += get(i) * len[i];
    }
    for (int i = 0; i < int(q); ++i) {
      res -= get(num[i]) * len[num[i]];
      len[num[i]] = w[i];
      res += get(num[i]) * len[num[i]];
      ans[i] = res / c(n, 3);
    }
  }
  void clear() { *this = Solution(); }
};
Solution sol;
int main() {
  cout.setf(ios::showpoint | ios::fixed);
  cout.precision(20);
  sol.read();
  sol.solve();
  sol.write();
  return 0;
}
