#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 100100;
ll sz[N], dpAll[N], dpBelow[N], up[N][18], dep[N], n;
vector<int> g[N];
void dfs1(int v, int p) {
  sz[v] = 1;
  up[v][0] = p;
  for (int i = 1; i < 18; i++) {
    up[v][i] = up[up[v][i - 1]][i - 1];
  }
  for (int u : g[v])
    if (u != p) {
      dep[u] = dep[v] + 1;
      dfs1(u, v);
      sz[v] += sz[u];
      dpBelow[v] += dpBelow[u] + sz[u];
    }
}
void dfs2(int v, int p) {
  if (v == 0)
    dpAll[v] = dpBelow[v];
  else
    dpAll[v] = dpAll[p] - sz[v] + (n - sz[v]);
  for (int u : g[v])
    if (u != p) {
      dfs2(u, v);
    }
}
int lift(int a, int k) {
  for (int i = 0; i < 18; i++) {
    if (k & (1 << i)) a = up[a][i];
  }
  return a;
}
int lca(int a, int b) {
  if (dep[a] < dep[b]) swap(a, b);
  a = lift(a, dep[a] - dep[b]);
  if (a == b) return a;
  for (int i = 17; i >= 0; i--) {
    if (up[a][i] != up[b][i]) {
      a = up[a][i], b = up[b][i];
    }
  }
  return up[a][0];
}
int dst(int a, int b) { return dep[a] + dep[b] - 2 * dep[lca(a, b)]; }
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int q;
  cin >> n >> q;
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v, u--, v--;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  dfs1(0, 0);
  dfs2(0, 0);
  while (q--) {
    int u, v;
    cin >> u >> v, u--, v--;
    int l = lca(u, v);
    if (l != u && l != v) {
      ll mul = sz[u] * sz[v];
      cout << fixed << setprecision(10)
           << (double)(dpBelow[u] * sz[v] + dpBelow[v] * sz[u] +
                       dst(u, v) * mul + mul) /
                  mul
           << '\n';
    } else {
      if (dep[u] < dep[v]) swap(u, v);
      int bfr = lift(u, dep[u] - dep[v] - 1);
      ll vCont = dpAll[v] - dpBelow[bfr] - sz[bfr];
      ll mul = sz[u] * (n - sz[bfr]);
      cout << fixed << setprecision(10)
           << (double)(dpBelow[u] * (n - sz[bfr]) + vCont * sz[u] +
                       dst(u, v) * mul + mul) /
                  mul
           << '\n';
    }
  }
}
