#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef double db;
typedef pair<int,int> pii;
#define fir first
#define sec second
#define rep(i,a,b) for (int i = (a) ; i <= (b) ; ++ i)
#define rrp(i,a,b) for (int i = (a) ; i >= (b) ; -- i)
#define gc() getchar()
template <typename tp>
inline void read(tp& x) {
  x = 0; char tmp; bool key = 0;
  for (tmp = gc() ; !isdigit(tmp) ; tmp = gc())
    key = (tmp == '-');
  for ( ; isdigit(tmp) ; tmp = gc())
    x = (x << 3) + (x << 1) + (tmp ^ '0');
  if (key) x = -x;
}
template <typename tp>
inline void ckmn(tp& x,tp y) {
  x = x < y ? x : y;
}
template <typename tp>
inline void ckmx(tp& x,tp y) {
  x = x < y ? y : x;
}

void solve() {
  int n;
  db mx = 0, b, c;
  read(n);
  rep (i, 1, n) {
    scanf("%lf%lf", &b, &c);
    mx = max(mx, (b + (1 - c) - b) / (b + (1 - c)));
  }
  printf("%.5lf\n", mx);
}
int main() {
  int T;
  read(T);
  while (T --)
    solve();
  return 0;
}