#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<vector>
#include<queue>
#include<set>
#include<map>
using namespace std;
typedef long long ll;
const int maxn = 2000 + 100;
const int mod = 1e9 + 7;
#define f(x) (x+x)
typedef long long ll;
const int INF = 0x3f3f3f3f;
int main(){
    int t;
    scanf("%d", &t);
    while(t--){
        int n;
        scanf("%d", &n);
        double ans = 0;
        for(int i = 0; i < n; ++i){
            double x, y;
            scanf("%lf%lf", &x, &y);
            ans = max(ans, (1-y)/(x+1-y));
        }
        printf("%.5f\n", ans);

    }
    return 0;
}