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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int textnum,tnum;
    double b,c;
    scanf("%d",&textnum);
    while(textnum--){
        scanf("%d",&tnum);
        double Discount=0;
        while(tnum--){
            scanf("%lf%lf",&b,&c);
            double d=(1-c)/(b+1-c);
            Discount=max(Discount,d);
        }
        cout.precision(5);
        cout.setf(ios::fixed);
        cout<<Discount<<endl;
    }
}