#include<iostream>
#include<cmath>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
#define ll long long
using namespace std;

int b[110];double c[111];
int main(){
    int t,n; 
    cin>>t;
    for(int ti=1;ti<=t;ti++){
        cin>>n;
        double ans=0;
        for(int i=1;i<=n;i++){
            cin>>b[i]>>c[i];
            double a=(1-c[i])/(b[i]+(1-c[i]));
            if(a>ans)ans=a;
        }
        printf("%.5lf\n",ans);
    //    cout<<ans<<endl;
    }
    return 0;
}