#include <iostream>
#include <cstring>
#include <utility>
#include <vector>
#include <cstdio>
#include <queue>
#include <algorithm>
#include <map>
#include <cmath>
#include <complex>
#include <array>
#include <ctime>
#include <cassert>
#include <set>
#include <iomanip>
#include <random>
#include <cstdlib>
#include <chrono>
#include <bitset>

using namespace std;


int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t; cin >> t;
    while (t--) {
        int n; cin >> n;
        int a; double b;
        double best = 0.0;

        for (int i = 0; i < n; i++) {
            cin >> a >> b;
            best = max(best, (1 - b) / (a + 1 - b));
        }
        cout << fixed << setprecision(5) << best << "\n";
    }

}