# include <bits/stdc++.h>
using namespace std;
# define rep(i,a,n) for (int i=a; i<=n; ++i)
# define per(i,a,n) for (int i=a; i>=n; --i)
# define bug puts("H");
# define pb push_back
# define mp make_pair
# define all(x) (x).begin(), (x).end()
# define SZ(x) (int)x.size()
# define fi first
# define se second
# define lch p<<1,l,mid
# define rch p<<1|1,mid+1,r
# define mem(a,b) memset(a,b,sizeof(a))
# define INF 1000000001
# define MOD 1000000007
typedef vector<int> Vi;
typedef long long i64;
typedef pair<int, int> Pi;
i64 powmod(i64 a, i64 b){i64 res=1;a%=MOD;assert(b>=0);for(;b;b>>=1){if(b&1)res=res*a%MOD;a=a*a%MOD;}return res;}
i64 Inv(i64 b){return powmod(b,(i64)MOD-2);}
const int N = 300005;
const double eps = 1e-9;
const double inf = 1e18;


int main ()
{
    int T;
    scanf("%d", &T);
    while (T--) {
        int n, b;
        double c;
        scanf("%d", &n);
        double ans = 0;
        rep(i,1,n) {
            scanf("%d%lf", &b, &c);
            ans = max(ans, (1-c)/(b+1-c));
        }
        printf("%.5f\n", ans);
    }
    return 0;
}