#include<bits/stdc++.h>
#define N 102
#define ll long long
using namespace std;
int T;
int n,b[N];
double c[N];

void solve() {
    double ans = 0.0;
    scanf("%d",&n);
    for(int i=0; i<n; i++) {
        scanf("%d%lf",&b[i],&c[i]);
        ans = max(ans,(1.0-c[i])/(b[i]*1.0+1.0-c[i]));
    }
    printf("%.5lf\n",ans);
}

int main() {
    scanf("%d",&T);
    while(T--) {
        solve();
    }
    return 0;
}