#include<bits/stdc++.h>
#define clr(x) memset(x,0,sizeof(x))
#define clrmax(x) memset(x,0x3f3f3f3f,sizeof(x))
#define clrmin(x) memset(x,-0x3f3f3f3f,sizeof(x))
#define pb push_back
#define LL long long
#define mod 1000000007
#define mp make_pair
using namespace std;
typedef pair<int,int> pii;
const int N = 1e2+10;
const int M = 3e5+10;
int T,n;
double b[N],c[N];
int main(){
    scanf("%d",&T);
    while(T --){
        scanf("%d",&n);
        for(int i=1;i<=n;i++){
        scanf("%lf%lf",&b[i],&c[i]);
        }
        double ans = (1 - c[1]) / (1 - c[1] + b[1]);
        for(int i=2;i<=n;i++){
        ans = max((1 - c[i]) / (1 - c[i] + b[i]),ans);
        }
        printf("%.5f\n",ans);
    }
    return 0;
}