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

int main() {
    int T;
    scanf("%d", &T);
    while (T--) {
        int n;
        scanf("%d", &n);
        double ans = 0;
        while (n--) {
            int b;
            double c;
            scanf("%d%lf", &b, &c);
            c = 1-c;
            ans = max(ans, c/(b+c));
        }
        printf("%.5f\n", ans);
    }
    return 0;
}