#include<bits/stdc++.h>
#define pb push_back
using namespace std;
typedef long long ll;

const int maxl=3e5+10;

int n,m,cas,k,cnt,tot;
double ans;
int b[maxl];double c[maxl];
char s[maxl];
bool in[maxl]; 

inline void prework()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
     scanf("%d%lf",&b[i],&c[i]);
} 

inline void mainwork()
{
    ans=0;
    for(int i=1;i<=n;i++)
        ans=max(ans,((1.0+b[i]-c[i])-b[i])/(1.0+b[i]-c[i]));
}

inline void print()
{
    printf("%.5f\n",ans);
}

int main()
{
    int t=1;
    scanf("%d",&t);
    for(cas=1;cas<=t;cas++)
    {
        prework();
        mainwork();
        print();
    }
    return 0;
}