#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<map>
#include<queue>
#include<vector>
#define ll long long
#define PI acos(-1.0)
#define F first
#define S second
#define pb push_back
#define debug(x); printf("debug%d\n",x);
#define des(x); printf("des:%s\n",x+1);
#define rep(f,t) for(int i=f;i<=t;i++)
const ll INF=0x3f3f3f3f3f3f3f3f;
const int inf=0x3f3f3f3f;
const ll mod=1e9+9;
using namespace std;
int t,n;
float a,b;
int main()
{
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        float ans=0.0;
        for(int i=1;i<=n;i++)
        {
            scanf("%f%f",&a,&b);
            float temp=1.0*(1.0-b)/(1.0*a+(1.0-b));
            ans=max(ans,temp);
        }
        printf("%.5f\n",ans);
    }
    return 0;
}