#include <iostream>
using namespace std;

int main() {
    int n;
    int a[10]={0},b[10]={0};
    while (scanf("%d",&n)!=EOF) { // 注意 while 处理多个 case
        int sum=0;
        float allscore=0;
        for(int i=0;i<n;i++){
            scanf("%d",&a[i]);
            sum+=a[i];
        }
        for(int i=0;i<n;i++){
            scanf("%d",&b[i]);
            if(b[i]>=90)allscore+=a[i]*4.0;
            else if(b[i]>=85)allscore+=a[i]*3.7;
            else if(b[i]>=82)allscore+=a[i]*3.3;
            else if(b[i]>=78)allscore+=a[i]*3.0;
            else if(b[i]>=75)allscore+=a[i]*2.7;
            else if(b[i]>=72)allscore+=a[i]*2.3;
            else if(b[i]>=68)allscore+=a[i]*2.0;
            else if(b[i]>=64)allscore+=a[i]*1.5;
            else if(b[i]>=60)allscore+=a[i]*1.0;
            else allscore+=0;
        }
        printf("%.2f\n",allscore/sum);

    }
}
// 64 位输出请用 printf("%lld")