#include<bits/stdc++.h>
using namespace std;

#define pb push_back
#define mp make_pair
#define ALL(x) (x).begin(),(x).end()
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
const int maxn = 2e3 + 70;
const int INF = 0x3f3f3f3f;
const ll inf = 0x3f3f3f3f3f3f3f3f;
const int MOD = 1e9 + 7;
const double eps = 1e-7;
const double PI = acos(-1.0);

int n;

int main(){
    //freopen("in.txt", "r", stdin);
    int T; cin>>T;
    while(T--){
        cin >> n;
        double ans = 0;
        for(int i=0;i<n;i++){
            double b, c; cin>>b>>c;
            ans = max(ans, (1-c)/(b+1-c));
        }
        printf("%.5f\n",ans);
    }
    return 0;
}