#include <bits/stdc++.h>
using namespace std;
const int maxn = 100100;
const int log_n = 19;
vector<int> G[maxn];
int D[maxn];
int up[maxn][log_n];
int tin[maxn], tout[maxn];
int size[maxn];
long long sumd[maxn];
void dfs(int v, int prev) {
  static int timer = 0;
  D[v] = D[prev] + 1;
  size[v] = 1;
  sumd[v] = 0;
  up[v][0] = prev;
  for (int i = 1; i < 18; i++) up[v][i] = up[up[v][i - 1]][i - 1];
  tin[v] = ++timer;
  for (int i = 0; i < (int)G[v].size(); i++) {
    int next = G[v][i];
    if (next == prev) continue;
    dfs(next, v);
    size[v] += size[next];
    sumd[v] += sumd[next] + size[next];
  }
  tout[v] = timer;
}
bool is_parent(int parent, int child) {
  return (tin[parent] <= tin[child] && tout[child] <= tout[parent]);
}
int lca(int u, int v) {
  if (is_parent(u, v)) return u;
  if (is_parent(v, u)) return v;
  for (int i = log_n - 1; i >= 0; i--)
    if (!is_parent(up[u][i], v)) u = up[u][i];
  return up[u][0];
}
int up_by(int u, int len) {
  for (int i = log_n - 1; i >= 0; --i) {
    if ((1 << i) <= len) {
      u = up[u][i];
      len -= 1 << i;
    }
  }
  return u;
}
long long sumu[maxn];
int colu[maxn];
void dfs2(int v, int pa, int col, long long sum) {
  sumu[v] = sum;
  colu[v] = col;
  for (int i = 0; i < G[v].size(); i++) {
    int to = G[v][i];
    if (to == pa) continue;
    dfs2(to, v, col + size[v] - size[to],
         sum + sumd[v] - size[to] - sumd[to] + col + size[v] - size[to]);
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  for (int _n(n - 1), i(0); i < _n; i++) {
    int a, b;
    cin >> a >> b;
    --a, --b;
    G[a].push_back(b);
    G[b].push_back(a);
  }
  D[0] = 0;
  dfs(0, 0);
  dfs2(0, 0, 0, 0);
  cout.precision(12);
  for (int _n(m), i(0); i < _n; i++) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    if (D[u] > D[v]) swap(u, v);
    int p = lca(u, v);
    int len = D[u] + D[v] - 2 * D[p];
    double ans = len + 1;
    if (p != u) {
      ans += (sumd[u] * 1.0) / size[u];
      ans += (sumd[v] * 1.0) / size[v];
    } else {
      int pp = up_by(v, D[v] - D[p] - 1);
      long long sum = sumd[u] + sumu[u];
      int col = size[u] + colu[u];
      sum -= sumd[pp] + size[pp];
      col -= size[pp];
      ans += (sum * 1.0) / col;
      ans += (sumd[v] * 1.0) / size[v];
    }
    cout << std::fixed << ans << endl;
  }
  return 0;
}
