int main()
{
    /*?????????????????????GPA????????????????????????????????? 
?????????? 
???? ?? 
90-100 4.0 
85-89  3.7 
82-84  3.3 
78-81  3.0 
75-77  2.7 
72-74  2.3 
68-71  2.0 
64-67  1.5 
60-63  1.0 
60?? 0 
1??????????=????*???? 
2?????=????????/???????? 
????????????A??????GPA?? 
????
??? ?????n?n<10?? 
??? ???????????????????? 
??? ?????????? 
??????????????
????
??????????????????2?????printf("%.2f",GPA);?*/
    int n1;
    cin>>n1;
    const int n=n1;
    int number[n],grade[n];
    float gpa[n],sum=0,sum1=0,average=0;
    int i;
    for(i=0;i<=n-1;i++)
    {
      cin>>number[i];
      }
    for(i=0;i<=n-1;i++)
    {
      cin>>grade[i];
      }
    for(i=0;i<=n-1;i++)
    {
      if((90<=grade[i])&&(grade[i]<=100))
      gpa[i]=4.0;

       if((85<=grade[i])&&(grade[i]<=89))
      gpa[i]=3.7;

       if((82<=grade[i])&&(grade[i]<=84))
     gpa[i]=3.3;

       if((78<=grade[i])&&(grade[i]<=81))
      gpa[i]=3.0;

       if((75<=grade[i])&&(grade[i]<=77))
      gpa[i]=2.7;

       if((72<=grade[i])&&(grade[i]<=74))
      gpa[i]=2.3;

       if((68<=grade[i])&&(grade[i]<=71))
       gpa[i]=2.0;

       if((64<=grade[i])&&(grade[i]<=67))
       gpa[i]=1.5;

       if((60<=grade[i])&&(grade[i]<=63))
       gpa[i]=1.0;

       if(grade[i]<60)
       gpa[i]=0;

       }
       for(i=0;i<=n-1;i++)
       {
          sum=sum+gpa[i]*number[i];
          sum1=sum1+number[i];
          }
          average=sum/sum1;
 
          printf("%.2f",average);
          
          return 0;
          }
                 
