#include <stdio.h>
int main(){
    int test;
    scanf("%d",&test);
    while(test>0){
        int n,i,j;
        scanf("%d",&n);
        int b[n];
        float c[n],a[n];
        for(i=0;i<n;i++){
            scanf("%d %f",&b[i],&c[i]);
            a[i]=(1.0-c[i])/(b[i]*1.0+1.0-c[i]);
        }
        float max=a[0];
        for(i=0;i<n;i++){
            if(a[i]>max){
                max=a[i];
            }
        }
        printf("%.5f\n",max);
        test--;
    }
    return 0;
}