#include <bits/stdc++.h>
using namespace std;
const unsigned long long inf = 0x3f3f3f3f3f3f3f3f;
const unsigned long long MAXN = 1e5 + 5;
unsigned long long cnt[MAXN];
vector<unsigned long long> adj[MAXN];
vector<unsigned long long> vis(MAXN, 0);
void dfs(unsigned long long v) {
  vis[v] = 1;
  if (adj[v].size() == 1 && v != 1) {
    cnt[v] = 1;
    return;
  }
  for (auto u : adj[v]) {
    if (!vis[u]) {
      dfs(u);
      cnt[v] += cnt[u];
    }
  }
  ++cnt[v];
}
unsigned long long nc2(unsigned long long n) {
  if (n < 2) return 0;
  return (n * (n - 1)) / 2;
}
long double nc3(unsigned long long n) {
  if (n < 3) return 0;
  return ((long double)n * (n - 1) * (n - 2)) / 6.0;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  unsigned long long n;
  cin >> n;
  pair<pair<unsigned long long, unsigned long long>, unsigned long long> cst[n];
  for (unsigned long long i = 0; i < n - 1; i++) {
    unsigned long long u, v, l;
    cin >> u >> v >> l;
    adj[v].push_back(u);
    adj[u].push_back(v);
    cst[i + 1] = {{u, v}, l};
  }
  dfs(1);
  long double ini = 0;
  long double wgt[n];
  fill(wgt, wgt + n, 0);
  long double ttl = nc3(n);
  for (unsigned long long i = 1; i < n; i++) {
    unsigned long long u = cst[i].first.first, v = cst[i].first.second;
    unsigned long long lft = min(cnt[u], cnt[v]);
    unsigned long long rgt = n - lft;
    wgt[i] += (long double)lft * nc2(rgt) + rgt * nc2(lft);
    wgt[i] *= 2;
    wgt[i] /= ttl;
    ini += wgt[i] * cst[i].second;
  }
  unsigned long long q;
  cin >> q;
  cout << fixed << setprecision(12);
  while (q--) {
    unsigned long long idx, x;
    cin >> idx >> x;
    ini -= wgt[idx] * (cst[idx].second - x);
    cst[idx].second = x;
    long double d = ini;
    cout << d << '\n';
  }
  return 0;
}
