#include <algorithm>
#include <array>
#include <cassert>
#include <iomanip>
#include <iostream>
#include <map>
#include <vector>

using namespace std;

void solve() {
  int n;
  cin >> n;
  int64_t amt;
  cin >> amt;
  long double denom = 0;
  for(int i = 0; i < n; i++) {
    int64_t x;
    cin >> x;
    denom += x;
  }
  cout << fixed << setprecision(67) << (amt * (long double)amt / denom) << "\n";
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int t;
  cin >> t;
  while(t--) solve();
}