#include <stdio.h>
#include <algorithm>

int n,b;
double c,ans;

void solve(){
    scanf("%d",&n);
    ans = 0;
    for(int i=1;i<=n;i++){
        scanf("%d%lf",&b,&c);
        c = 1-c;
        ans = std::max(ans,c/(b+c));
    }
    printf("%.5lf\n",ans);
}

int main(){
    int T; scanf("%d",&T);
    while(T--) solve();
}