/*
?? - 1017 ????   

?? ????05  
?? 
?????????????????????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 main()
{
	int n,xuefen[10],defen[10],i=0;
	float GPA=0,gpa=0,fen=0;
	scanf("%d",&n);
	for(i=0;i<n;i++)
	{
		scanf("%d",&xuefen[i]);
	}
    for(i=0;i<n;i++)
	{
		scanf("%d",&defen[i]);
	}
    for(i=0;i<n;i++)
	{
		fen+=xuefen[i];
		if(defen[i]>=90)
		{
			gpa+=4.0*xuefen[i];
		}
		else if(defen[i]>=85&&defen[i]<=89)
		{
			gpa+=3.7*xuefen[i];
		}
		else if(defen[i]>=82&&defen[i]<=84)
		{
			gpa+=3.3*xuefen[i];
		}
		else if(defen[i]>=78&&defen[i]<=81)
		{
			gpa+=3.0*xuefen[i];
		}
		else if(defen[i]>=75&&defen[i]<=77)
		{
			gpa+=2.7*xuefen[i];
		}
		else if(defen[i]>=72&&defen[i]<=74)
		{
			gpa+=2.3*xuefen[i];
		}
		else if(defen[i]>=68&&defen[i]<=71)
		{
			gpa+=2.0*xuefen[i];
		}
		else if(defen[i]>=64&&defen[i]<=67)
		{
			gpa+=1.5*xuefen[i];
		}
		else if(defen[i]>=60&&defen[i]<=63)
		{
			gpa+=1.0*xuefen[i];
		}
		
	}
	GPA=gpa/fen;
	printf("%.2f",GPA);
}
