#include <iostream>
#include<vector>
#include<algorithm>

using namespace std;

vector<float> calculate()
{
    int gNum;
    cin >> gNum;
    vector<float> output;
    for (int i = 0; i < gNum; i++)
    {
        float res = 0;
        int cNum;
        cin >> cNum;
        int b;
        float c;
        for (int j = 0; j < cNum; j++)
        {
            cin >> b;
            cin >> c;
            float temp = (1 - c) / (b + 1 - c);
            res = max(res, temp);
        }
        output.push_back(res);
    }
    return output;
}

int main()
{
    vector<float> res = calculate();
    for (int i = 0; i < res.size(); i++)
    {
        //cout << res[i];
        printf("%.5f\n", res[i]);
    }
    return 0;
}