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

int main(){
    int T;
    cin>>T;
    while(T--){
        int n;
        cin>>n;
        double ans=0;
        for(int i=1;i<=n;++i){
            double b,c;
            cin>>b>>c;
            ans=max(ans,(1.0-c)/(b+1.0-c));
        }
        printf("%.5f\n",ans);
    }
    
    
    return 0;
}