#include <bits/stdc++.h>
using namespace std;
int n, depth[100011], parent[100011], dp[20][100011], subsz[100011];
long long dist[100011], pdist[100011];
vector<int> adj[100011];
void dfs(int u, int h, int p) {
  parent[u] = p;
  depth[u] = h;
  subsz[u] = 1;
  dist[u] = 0LL;
  for (int i = 0; i < adj[u].size(); i++) {
    int k = adj[u][i];
    if (k == p) continue;
    dfs(k, h + 1, u);
    subsz[u] += subsz[k];
    dist[u] += dist[k] + subsz[k];
  }
}
void pre(int n) {
  int i;
  for (int i = 0; i < 20; i++)
    for (int j = 0; j <= n; j++) dp[i][j] = -1;
  for (i = 1; i <= n; i++) dp[0][i] = parent[i];
  for (i = 1; (1 << i) <= n; i++) {
    for (int j = 1; j <= n; j++) dp[i][j] = dp[i - 1][dp[i - 1][j]];
  }
}
int lca(int u, int v) {
  if (depth[u] < depth[v]) swap(u, v);
  int diff = depth[u] - depth[v];
  for (int i = 0; i < 20; i++)
    if ((diff >> i) & 1) u = dp[i][u];
  if (u == v) return u;
  for (int i = 19; i >= 0; i--) {
    if (dp[i][u] != dp[i][v]) {
      u = dp[i][u];
      v = dp[i][v];
    }
  }
  return dp[0][u];
}
void dfs1(int u, int p) {
  if (u != 1) {
    long long c = n - subsz[u];
    pdist[u] = pdist[p] + (n - subsz[p]);
    pdist[u] += ((dist[p] - (subsz[u] + dist[u])) + (subsz[p] - subsz[u]));
  }
  for (int i = 0; i < adj[u].size(); i++) {
    if (adj[u][i] == p) continue;
    dfs1(adj[u][i], u);
  }
}
int func(int u, int v) {
  int d = depth[v] - depth[u];
  d--;
  for (int i = 19; i >= 0; i--) {
    if ((d >> i) & 1) v = dp[i][v];
  }
  return v;
}
int main() {
  int m, i, j;
  scanf("%d %d", &n, &m);
  for (i = 0; i < n - 1; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    adj[u].push_back(v);
    adj[v].push_back(u);
  }
  dfs(1, 0, -1);
  pre(n);
  dfs1(1, -1);
  for (i = 0; i < m; i++) {
    int u, v;
    scanf("%d %d", &u, &v);
    int x = lca(u, v);
    if (x == u) {
      int y = func(u, v);
      long long ans = (long long)(depth[v] - depth[u]) *
                      ((long long)subsz[v] * (long long)(n - subsz[y]));
      ans += (dist[v] * (long long)(n - subsz[y]));
      long long d = pdist[u] + dist[u] - dist[y] - subsz[y];
      ans += (d * (long long)(subsz[v]));
      ans += ((long long)subsz[v] * (long long)(n - subsz[y]));
      double an = (double)ans /
                  (double)((long long)subsz[v] * (long long)(n - subsz[y]));
      printf("%.8lf\n", an);
    } else if (x == v) {
      swap(u, v);
      int y = func(u, v);
      long long ans = (long long)(depth[v] - depth[u]) *
                      ((long long)subsz[v] * (long long)(n - subsz[y]));
      ans += (dist[v] * (long long)(n - subsz[y]));
      long long d = pdist[u] + dist[u] - dist[y] - subsz[y];
      ans += (d * (long long)(subsz[v]));
      ans += ((long long)subsz[v] * (long long)(n - subsz[y]));
      double an = (double)ans /
                  (double)((long long)subsz[v] * (long long)(n - subsz[y]));
      printf("%.8lf\n", an);
    } else {
      long long ans = (long long)(depth[v] + depth[u] - 2 * depth[x]) *
                      ((long long)subsz[v] * (long long)subsz[u]);
      ans += (dist[u] * subsz[v]);
      ans += (dist[v] * subsz[u]);
      ans += ((long long)subsz[v] * (long long)(subsz[u]));
      double an =
          (double)ans / (double)((long long)subsz[v] * (long long)subsz[u]);
      printf("%.8lf\n", an);
    }
  }
  return 0;
}
