#include<iostream>
#include<iomanip>
using namespace std;
#define INF 0X3f3f3f3f
int b[105];
double c[105];
int main() {
    int T,n; cin >> T;
    while (T--) {
        double max = -INF;
        cin >> n;
        for (int i = 0; i < n; i++) {
            cin >> b[i] >> c[i];
        }
        for (int i = 0; i < n; i++) {
            if (double(1.0 - c[i]) / double(1.0 - c[i] + b[i]) > max)
                max = double(1.0 - c[i]) / double(1.0 - c[i] + b[i]);
        }cout <<fixed<<setprecision(5)<< max << endl;
    }
    return 0;
}