#include <cstdio>
#include <algorithm>
#include <iostream>
#include <cmath>
#include <cstring>
#include <vector>
#include <queue>
#include <string>
#include <set>
using namespace std;
typedef long long ll;
int main()
{
    int t;
    cin >> t;
    while(t--)
    {
        int n;
        cin >> n;
        double ans=0;
        for (int i=1;i<=n;i++)
        {
            int x;
            double y;
            cin >> x >> y;
            double sum = (1.0-y)/(x+1.0-y);
            ans=max(sum,ans);
        }
        printf("%.5f\n",ans);
    }
    return 0;
}