#include <cstdio>
#include <iostream>
#include <cstring>
#include <queue>
#include <cmath>
#include <set>
#include <algorithm>
#include <map>
#include <vector>
#define mod 1000000007
using namespace std;
typedef long long ll;

const int N = 106;
const double inf = 0x3f3f3f3f;
const double eps = 1e-6;


int main()
{
    int t, n;
    double b, c, ans;
    scanf("%d", &t);
    while(t--){
        scanf("%d", &n);
        ans = 0;
        while(n--){
            scanf("%lf%lf", &b, &c);
            double tp = (1.0-c)/(b+1.0-c);
            if(ans < tp)
                ans = tp;
        }
        printf("%.5lf\n", ans);
    }
    return 0;
}