#include<bits/stdc++.h> 
using namespace std;
int main()
{
    int t,n,i;
    float b,c;
    cin>>t;
    while(t--)
    {
        cin>>n;
        float max=0;
        for(i=0;i<n;++i)
        {
            cin>>b>>c;
            float m=(1.0-c)/(b+1.0-c);
            if(m>max)max=m;
            
        }
        printf("%.5f\n",max);
    } 
}