#include <cstdio>
#include <algorithm>

// using i64 = long long;

// const int maxn = 200000;

// #define LOG(info...) fprintf(stderr, "log: " info)

// inline int Min(const int &x, const int &y) {
//     return x < y ? x : y;
// }
// inline int Max(const int &x, const int &y) {
//     return x > y ? x : y;
// }

inline int input() {
    static int p;
    scanf("%d", &p);
    return p;
}
inline double inputf() {
    static double p;
    scanf("%lf", &p);
    return p;
}

int main() {
    for (int T = input(); T; --T) {
        const int n = input();
        double ans = 0;
        for (int i = 1; i <= n; ++i) {
            const int b = input(); const double c = inputf();
            ans = std::max(ans, (1.0 - c) / (b + (1.0 - c)));
        }
        printf("%.5lf\n", ans);
    }

    return 0;
}