
int main(){

int s,i,z=0,q,n,w;
float a=0,d;
scanf("%d",&n);int grade[n],num[n];float g[n];
for(i=0;i<n;i++){
                  scanf("%d",&num[i]);
                  }for(i=0;i<n;i++)
                  {scanf("%d",&grade[i]);}
for(i=0;i<n;i++){
          if(grade[i]<101&&grade[i]>89)g[i]=4.0;
    if(grade[i]<90&&grade[i]>84)
    g[i]=3.7;if(grade[i]<85&&grade[i]>81)
    g[i]=3.3;if(grade[i]<82&&grade[i]>77)
    g[i]=3.0;if(grade[i]<78&&grade[i]>74)
    g[i]=2.7;if(grade[i]<75&&grade[i]>71)
    g[i]=2.3;if(grade[i]<72&&grade[i]>67)
    g[i]=2.0;if(grade[i]<68&&grade[i]>63)
    g[i]=1.5;if(grade[i]<64&&grade[i]>59)
    g[i]=1.0;if(grade[i]<60)
    g[i]=0;}
    for(i=0;i<n;i++){
              a+=g[i]*num[i];
              z+=num[i];
              }       
               d=a/z;
               printf("%.2f",d);                

return 0;}