#include <bits/stdc++.h>
using namespace std;
const int N = 100005;
int n, m;
vector<int> g[N];
long long sz[N], dp[N], sum[N];
int dep[N], fa[N][20];
void dfs1(int u, int p) {
  fa[u][0] = p;
  dep[u] = dep[p] + 1;
  for (int i = 1; i < 20; i++) fa[u][i] = fa[fa[u][i - 1]][i - 1];
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == p) continue;
    dfs1(v, u);
    dp[u] += dp[v];
    sz[u] += sz[v];
  }
  dp[u] += sz[u];
  sz[u]++;
}
void dfs2(int u, int p, long long tot) {
  sum[u] = tot + dp[u];
  for (int i = 0; i < g[u].size(); i++) {
    int v = g[u][i];
    if (v == p) continue;
    dfs2(v, u, tot + dp[u] - dp[v] - sz[v] + n - sz[v]);
  }
}
int lca(int u, int v) {
  int d = dep[u] - dep[v];
  for (int i = 0; i < 20; i++)
    if (d & (1 << i)) u = fa[u][i];
  if (u == v) return u;
  for (int i = 19; i >= 0; i--) {
    if (fa[u][i] == fa[v][i]) continue;
    u = fa[u][i];
    v = fa[v][i];
  }
  return fa[u][0];
}
int main() {
  scanf("%d%d", &n, &m);
  int u, v;
  for (int i = 1; i <= n - 1; i++) {
    scanf("%d%d", &u, &v);
    g[u].push_back(v);
    g[v].push_back(u);
  }
  dfs1(1, 1);
  dfs2(1, 1, 0);
  while (m--) {
    scanf("%d%d", &u, &v);
    if (dep[u] < dep[v]) swap(u, v);
    int rt = lca(u, v);
    long long sum1, sum2, sz1, sz2;
    long long len = dep[u] + dep[v] - 2 * dep[rt] + 1;
    if (rt == v) {
      rt = u;
      for (int i = 0; i < 20; i++) {
        if ((dep[u] - dep[v] - 1) & (1 << i)) rt = fa[rt][i];
      }
      sum1 = dp[u];
      sum2 = sum[v] - dp[rt] - sz[rt];
      sz1 = sz[u];
      sz2 = n - sz[rt];
    } else {
      sum1 = dp[u];
      sum2 = dp[v];
      sz1 = sz[u];
      sz2 = sz[v];
    }
    printf("%.12f\n",
           (sum1 * sz2 + sum2 * sz1 + len * sz1 * sz2) * 1.0 / (sz1 * sz2));
  }
  return 0;
}
