#include <bits/stdc++.h>

using namespace std;

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int n;
        double b[105],c[105];
        scanf("%d",&n);
        for(int i=1; i<=n; i++)
        {
            scanf("%lf%lf",&b[i],&c[i]);
        }
        double maxx = -1;
        for(int i=1; i<=n; i++)
        {
            maxx = max(maxx,(1-c[i])/(1-c[i]+b[i]));
        }
        printf("%.5lf\n",maxx);

    }
    return 0;
}