#include<bits/stdc++.h>
#define ls ch[x][0]
#define rs ch[x][1]
#define ll long long
using namespace std;

inline ll read(){
    ll num=0,neg=1;char c=getchar();
    while(!isdigit(c)){if(c=='-')neg=-1;c=getchar();}
    while(isdigit(c)){num=(num<<3)+(num<<1)+c-'0';c=getchar();}
    return num*neg;
}

int T,n,b;
double c;

int main(){
    T=read();
    while(T--)
    {
        n=read();double ans,res=0.0;
        for(int i=1;i<=n;i++)
        {
            b=read(),cin>>c;
            c=1.0-c;
            ans=c/(b*1.0+c);
            if(ans>res)res=ans;
        }
        printf("%.5lf\n",res);
    }return 0;
}