#include <bits/stdc++.h>


using namespace std;

const int N = 2010;

int b[110];
double c[110];

int main()
{
    int T;
    scanf("%d",&T);
    while(T--) {
        int n;
        scanf("%d",&n);
        double ans = 1;
        for(int i =0;i<n;i++) {
            scanf("%d %lf",&b[i],&c[i]);
            ans = min(ans, b[i]/(1+b[i]-c[i]));
        }
        printf("%.5f\n",1-ans);
    }
    return 0;
}