#include <cstdio>
#include <algorithm>
#include <iostream>
using namespace std;
typedef long long ll;
int n,m;
int main(){
    int t;scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        double x,y,mx = 0;
        for(int i = 0;i < n;i++){
            scanf("%lf%lf",&x,&y);
            //cout<<(1.0-y)<<"/"<<(x + 1.0-y)<<endl;
            mx = max(mx,(1.0-y)/(x + 1.0-y));
        }
        printf("%.5f\n",mx);
    }
    return 0;
}