#include<bits/stdc++.h>

using namespace std;
const int M=105;
int n;
void solve(){
    double ans=0;
    scanf("%d",&n);
    for(;n;--n){
        double a,b,c;
        scanf("%lf%lf",&b,&c);
        a=(1-c)/(b+1-c);
        ans=max(ans,a);
    }
    printf("%.5lf\n",ans);
}
int main(){
    int t;scanf("%d",&t);
    for(;t;--t)solve();
    return 0;
}