#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

template<class Type>
inline void R(Type &x) {
    int c = getchar();
    bool neg = 0;
    for (; c < 48 || c > 57; c = getchar())if (c == '-')neg = true;
    for (x = 0; c > 47 && c < 58; x = (Type) 10 * x + c - 48, c = getchar());
    if (neg)x = -x;
}

int n;
double perc;

int main() {
    int T;
    R(T);
    while (T--) {
        R(n);
        perc = 0.0;
        for (int i = 1; i <= n; ++i) {
            double b, c;
            scanf("%lf%lf", &b, &c);
            perc = max(perc, (1 - c) / (b + 1 - c));
        }
        printf("%.5lf\n",perc);
    }
    return 0;
}