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

int main()
{
    int T, n;
    double min = 0, c, b, tmp;
    cin >> T;
    for (int i = 0; i < T; i++)
    {
        cin >> n;
        for (int j = 0; j < n; j++)
        {
            cin >> b >> c;
            c = 1 - c;
            tmp = c / (b + c);
            if (tmp > min)
                min = tmp;
        }
        printf("%.5lf\n", min);
        min = 0;
    }
}