#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
#define F(N,S,T) for(int N=(S);N<=(T);N++)

int calc(int b,int c){
    return (200001*c+100*b)/(200*b+2*c);
}

void work(){
    int n;
    cin>>n;
    int ans=-1e9;
    while(n--){
        int b;
        double c;
        cin>>b>>c;
        ans=max(ans,calc(b,round((1-c)*100)));
    }
    printf("%d.%05d\n",ans/100000,ans%100000);
}

int main(){
    ios::sync_with_stdio(false);
    int t;
    cin>>t;
    while(t--){
        work();
    }
    return 0;
}