#include <bits/stdc++.h>
using namespace std;
vector<string> vec_splitter(string s) {
  s += ',';
  vector<string> res;
  while (!s.empty()) {
    res.push_back(s.substr(0, s.find(',')));
    s = s.substr(s.find(',') + 1);
  }
  return res;
}
void debug_out(vector<string> __attribute__((unused)) args,
               __attribute__((unused)) int idx,
               __attribute__((unused)) int LINE_NUM) {
  cerr << endl;
}
template <typename Head, typename... Tail>
void debug_out(vector<string> args, int idx, int LINE_NUM, Head H, Tail... T) {
  if (idx > 0)
    cerr << ", ";
  else
    cerr << "Line(" << LINE_NUM << ") ";
  stringstream ss;
  ss << H;
  cerr << args[idx] << " = " << ss.str();
  debug_out(args, idx + 1, LINE_NUM, T...);
}
const int LOG = 24;
const int NN = (int)1e5 + 5;
const int MaxM = (int)10000 + 5;
const int MOD = (int)1e9 + 7;
const int INF = INT_MAX - 1;
int mul(int x, int y) { return (1LL * x * y) % MOD; }
int add(int x, int y) {
  long long res = x;
  res += y;
  return (res % MOD + MOD) % MOD;
}
void norm_add(int& x, int y) {
  x += y;
  if (x >= MOD) x -= MOD;
}
int fast_pow(int x, long long y) {
  if (y == 0) return 1;
  if (y & 1)
    return mul(x, fast_pow(x, y - 1));
  else {
    int aux = fast_pow(x, y >> 1);
    return mul(aux, aux);
  }
}
int inv(int x) { return fast_pow(x, MOD - 2); }
int two(int x) { return 1 << x; }
bool contain(int mask, int bit) { return (mask & two(bit)) > 0; }
int gcd(int a, int b) { return b == 0 ? a : gcd(b, a % b); }
int n;
vector<int> adj[NN], edge_idx[NN];
int sub[NN];
int w[NN];
double denom[NN];
double ans;
double n3;
double choose2(double x) { return (x * (x - 1.0)) / 2.0; }
double choose3(double x) { return (x * (x - 1.0) * (x - 2.0)) / 6.0; }
void dfs(int node, int f) {
  sub[node] = 1;
  for (int i = 0; i < ((int)adj[node].size()); i++) {
    int child = adj[node][i];
    if (child == f) continue;
    dfs(child, node);
    sub[node] += sub[child];
    int idx = edge_idx[node][i];
    int A = sub[child], B = n - A;
    denom[idx] = (choose2(A) * B + A * choose2(B));
    ans += w[idx] * 2.0 * denom[idx] / n3;
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  scanf("%d", &n);
  for (int i = 0; i < n - 1; i++) {
    int x, y;
    scanf("%d%d%d", &x, &y, &w[i]);
    adj[x].push_back(y);
    edge_idx[x].push_back(i);
    adj[y].push_back(x);
    edge_idx[y].push_back(i);
  }
  n3 = choose3(n);
  ans = 0.0;
  dfs(1, 0);
  42;
  int q;
  scanf("%d", &q);
  while (q--) {
    int idx, new_w;
    scanf("%d%d", &idx, &new_w);
    idx--;
    ans -= (w[idx] - new_w) * 2.0 * denom[idx] / n3;
    w[idx] = new_w;
    printf("%.10f\n", ans);
  }
  return 0;
}
