#include<iostream>
#include<string.h>
#include<stdio.h>
#include<iomanip>
#include <stdlib.h>
#include<algorithm>
using namespace std;
int main()
{
    int test;
    cin>>test;
    while(test--)
    {
        int n,b[100];
        double c[100],m=0,x;
        cin>>n;
        for(int i=0;i<n;i++){
            cin>>b[i]>>c[i];
        }
        for(int i=0;i<n;i++){
            x=(1-c[i])/(b[i]+1-c[i]);
            if(x>m)m=x;
        }
        cout<<setiosflags(ios::fixed)<<setprecision(5)<<m<<endl;;
    }
    return 0;
}