#include <bits/stdc++.h>
using namespace std;
const int MAXN = (int)1e5 + 10;
int n, q, p[MAXN][20];
vector<int> adj[MAXN], child[MAXN];
long long d[MAXN], s[MAXN], c[MAXN], dp[MAXN];
bool fre[MAXN];
void DFS(int u) {
  fre[u] = false;
  s[u] = d[u];
  c[u] = 1;
  for (int i = 0; i < (int)adj[u].size(); ++i) {
    int v = adj[u][i];
    if (fre[v]) {
      p[v][0] = u;
      d[v] = d[u] + 1;
      child[u].push_back(v);
      DFS(v);
      s[u] += s[v];
      c[u] += c[v];
    }
  }
}
void InitLCA() {
  for (int j = 1; 1 << j <= n; ++j)
    for (int i = 1; i <= n; ++i) p[i][j] = p[p[i][j - 1]][j - 1];
}
int LCA(int u, int v) {
  if (d[u] < d[v]) swap(u, v);
  int log = 0;
  while (1 << log <= d[u]) log++;
  log--;
  for (int i = log; i >= 0; --i)
    if (d[u] - (1 << i) >= d[v]) u = p[u][i];
  if (u == v) return u;
  for (int i = log; i >= 0; --i)
    if (p[u][i] != p[v][i]) {
      u = p[u][i];
      v = p[v][i];
    }
  return p[u][0];
}
void DP(int u, long long k) {
  dp[u] = s[u] - d[u] * c[u] + d[u] * (n - c[u]) + k;
  k -= d[u];
  for (int i = 0; i < (int)child[u].size(); ++i) {
    int v = child[u][i];
    k += s[v] - c[v] * d[u] * 2;
  }
  for (int i = 0; i < (int)child[u].size(); ++i) {
    int v = child[u][i];
    DP(v, k - (s[v] - c[v] * d[u] * 2));
  }
}
int kthParent(int u, int k) {
  for (int i = 20; i >= 0; --i)
    if (k >= (1 << i)) u = p[u][i], k -= (1 << i);
  return u;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> q;
  for (int i = 1; i <= n - 1; ++i) {
    int u, v;
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  memset(fre, true, sizeof fre);
  DFS(1);
  InitLCA();
  DP(1, 0);
  while (q--) {
    int u, v;
    cin >> u >> v;
    int t = LCA(u, v);
    if (t != u && t != v) {
      double a = (s[u] - d[t] * c[u]) * c[v] + c[u] * (s[v] - d[t] * c[v]) +
                 c[u] * c[v];
      double b = c[u] * c[v];
      cout << fixed << setprecision(8) << a / b << "\n";
    } else {
      if (t == v) swap(u, v);
      int uu = kthParent(v, d[v] - d[u] - 1);
      double a = (s[v] - d[u] * c[v]) * (n - c[uu]) +
                 (dp[u] - s[uu] + d[u] * c[uu]) * c[v] + (n - c[uu]) * c[v];
      double b = (n - c[uu]) * c[v];
      cout << fixed << setprecision(8) << a / b << "\n";
    }
  }
  return 0;
}
