#include <map>
#include <set>
#include <array>
#include <cmath>
#include <deque>
#include <bitset>
#include <random>
#include <string>
#include <vector>
#include <cassert>
#include <complex>
#include <iomanip>
#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>

using namespace std;


using ld = long double;

const ld PI = atan2l(0, -1);

ld D(ld a, ld p) {
    cerr << a << " " << p << endl;
    return a * logl(a / p) + (1 - a) * logl((1 - a) / (1 - p));
}

ld F(int n, ld p, int k) {
    if (k == n + 1) {
        return -1e18;
    }
    if (k == n) {
        return logl(p) * n;
    }
    if (k == 0) {
        return 0;
    }
    return -n * D((ld)k / n, p);
}

void solve() {
    int n, k;
    cin >> n >> k;
    ld ans = logl(3ll * k + 1);
    k = min(k, n);
    if (3ll * k <= 2ll * n) {
        ans -= F(n, (ld)1 / 3, n - k);
    } else {
        ld p = F(n, (ld)2 / 3, k + 1);
        p = logl(1 - expl(p));
        ans -= p;
    }
    cout << ans << "\n";
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);

  cout << fixed << setprecision(20);

  int tst;
  cin >> tst;
  while (tst--) {
    solve();
  }


  return 0;
}