#pragma GCC optimize("-Ofast","-funroll-all-loops")
#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=110;
int n;
void solve(){
    double b,c,mx=0.0; cin>>n;
    for(int i=1;i<=n;i++){
        cin>>b>>c;
        mx=max(mx,(1-c)/(b+1-c));
    }
    printf("%.5lf\n",mx);
}
signed main(){
    int T; cin>>T; while(T--) solve();
    return 0;
}