#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 7;
const int LG = 18;
long long dp[N], up[N];
int cnt[N], d[N], par[N][LG];
vector<int> adj[N];
int n, m;
void dfs(int v, int p) {
  cnt[v] = 1;
  for (auto u : adj[v])
    if (u != p) {
      d[u] = d[v] + 1;
      par[u][0] = v;
      for (int i = 1; i < LG; i++) par[u][i] = par[par[u][i - 1]][i - 1];
      dfs(u, v);
      cnt[v] += cnt[u];
      dp[v] += dp[u] + cnt[u];
    }
  for (int i = 0; i < (int)adj[v].size(); i++)
    if (adj[v][i] == p) {
      adj[v].erase(adj[v].begin() + i);
      break;
    }
}
void DFS(int v) {
  for (auto u : adj[v]) {
    up[u] = up[v] + dp[v] - (dp[u] + cnt[u]) + (n - cnt[u]);
    DFS(u);
  }
}
int get_par(int v, int a) {
  for (int i = 0; i < LG; i++)
    if ((a >> i) & 1) v = par[v][i];
  return v;
}
int lca(int v, int u) {
  if (d[u] > d[v]) swap(u, v);
  v = get_par(v, d[v] - d[u]);
  if (v == u) return v;
  for (int i = LG - 1; i >= 0; i--)
    if (par[v][i] != par[u][i]) v = par[v][i], u = par[u][i];
  return par[v][0];
}
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> m;
  for (int i = 1; i < n; i++) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    adj[v].push_back(u);
    adj[u].push_back(v);
  }
  dfs(0, -1);
  DFS(0);
  cout << setprecision(12) << fixed;
  while (m--) {
    int u, v;
    cin >> u >> v;
    u--, v--;
    if (d[u] > d[v]) swap(u, v);
    int w = lca(u, v);
    long long sum = 0;
    long long way = 0;
    if (w == u) {
      int badver = get_par(v, d[v] - d[w] - 1);
      sum = 1LL * (up[badver] - (n - cnt[badver])) * cnt[v] +
            1LL * dp[v] * (n - cnt[badver]);
      way = 1LL * cnt[v] * (n - cnt[badver]);
    } else {
      sum = 1LL * dp[v] * cnt[u] + 1LL * dp[u] * cnt[v];
      way = 1LL * cnt[v] * cnt[u];
    }
    cout << d[v] + d[u] - 2 * d[w] + 1 + 1.0 * sum / way << "\n";
  }
  return 0;
}
