#include <cstdio>
#include <algorithm>
using namespace std;

int n;

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