#include <bits/stdc++.h>
using namespace std;

int main() {
    int t;
    cin >> t;
    while (t--) {
        int n;
        cin >> n;
        vector<int> b(n);
        vector<double> c(n);
        for (int i = 0; i < n; i++) {
            cin >> b[i] >> c[i];
        }
        double res = 0;
        for (int i = 0; i < n; i++) {
            double tmp = (1.0-c[i]) / (b[i]*1.0 + 1-c[i]);
            if (tmp-res > 1e-6) {
                res = tmp;
            }
        }
        printf("%.5lf\n", res);
    }
}