#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define rep(i, a, b) for(int i = (a); i < (b); i++)
#define per(i, a, b) for(int i = (b) - 1; i >= (a); --i)
#define de(x) cout << #x << " = " << x << endl
#define dd(x) cout << #x << " = " << x << " "
#define endl '\n'
#define pw(x) (1ll<<(x))
#define all(x) x.begin(), x.end()
#define sz(x) (int)x. size()
typedef long long ll;
typedef double db;
typedef pair<int, int> pii;
typedef vector<int> vi;

int t;
int n;
double b,c;

int main()
{
    std::ios::sync_with_stdio(0);
    std::cin.tie(0);

    while(cin>>t)
    {
        while(t--)
        {
            cin>>n;
            double ans=0;
            rep(i,1,n+1)
            {
                cin>>b>>c;
                ans=max(ans,(1-c)/(b+(1-c)));
            }
            printf("%.5lf\n",ans);
        }
    }

    return 0;
}