#include<iostream>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<map>
using namespace std;

int main(){
    int test;
    cin>>test;
    while(test--){
        int n;
        cin>>n;
        int b[n];
        double c[n];
        double d[n];
        for(int i=0;i<n;i++){
            cin>>b[i]>>c[i];
            double t=1-c[i];
            d[i]=t*1.0/(b[i]+t);
        }
        sort(d,d+n);
        printf("%.5f\n",d[n-1]);
    } 
    return 0;
}