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

int main() {
    ios::sync_with_stdio(0);
    int T; cin >> T;
    while (T--) {
        int n; cin >> n;
        double ans = 0;
        for (int i = 1; i <= n; i++) {
            double b, c;
            cin >> b >> c;
            c = 1.0 - c;
            if (c / (b + c) > ans) {
                ans = max(ans, c / (b + c));
            }
        }
        printf("%.5f\n", ans);
    }
}