#include<bits/stdc++.h>
using namespace std;
int main(){
    int T, n;
    scanf("%d", &T);
    while (T--){
        scanf("%d", &n);
        double mx = 0;
        for (int i = 1; i <= n; i++) {
            int b; double c;
            scanf("%d%lf", &b, &c);
            double rate = (1 - c)/(b + 1 - c);
            if (rate > mx) {
                mx = rate;
            
            }
        }
        printf("%.5lf\n", mx);
    }
}