#include <bits/stdc++.h>
#include <iostream>
#include <cstdio>
#define LL long long
#define inf 0x3f
const int mod = 1e9+7;
using namespace std;


int main()
{
    double q,p,x,y;
    int t,n;
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        q = -10;
        for(int i = 1; i <= n; i++){
            scanf("%lf%lf",&x,&y);
            p = 1.0 * (1 - y) / (x + 1 - y);
            q = max(p,q);
        }
        printf("%.5f\n",q);
    }
    return 0;
}