#include<bits/stdc++.h>
#define Max(a,b) ((a<b)&&(a=b))
#define Min(a,b) ((a>b)&&(a=b))
#define rep(i,a,b) for(int i=a,i##end=b;i<=i##end;++i)
#define drep(i,a,b) for(int i=a,i##end=b;i>=i##end;--i)
#define erep(i,a) for(int i=hd[a],y;(y=to[i]);i=nxt[i])
using namespace std;
typedef long long ll;
char C;
inline int rd() {
    int res=0,f=1;
    while(C=getchar(),C<48||C>57)if(C=='-')f=0;
    do res=(res<<3)+(res<<1)+(C^48);
    while(C=getchar(),C>=48&&C<=57);
    if(f)return res;
    return -res;
}
int b[105];
double c[105];
int main() {
    int T=rd();
    while(T--){
        int n=rd();
        double ans=0;
        rep(i,1,n){
            scanf("%d%lf",&b[i],&c[i]);
            double t=(1-c[i])/(b[i]+1-c[i]);
            Max(ans,t);
        }
        printf("%.5f\n",ans);
    }
}