

int main()
{
    int i,j,k,n;
	scanf("%d",&n);
	int a[9]={0,0,0,0,0,0,0,0,0};
	for(i=0;i<n;i++)
	{scanf("%d",&a[i]);}
	int b[9]={0,0,0,0,0,0,0,0,0};
	for(j=0;j<n;j++)
	{scanf("%d",&b[j]);}
	double c[9]={0,0,0,0,0,0,0,0,0};
	for(k=0;k<n;k++)
	{if(b[k]<=100&&b[k]>=90)
	    c[k]=4.0*a[k];
	else 
		if(b[k]<=89&&b[k]>=85)
			c[k]=3.7*a[k];
		else
		    if(b[k]<=84&&b[k]>=82)
			   c[k]=3.3*a[k];
	        else 
	  	        if(b[k]<=81&&b[k]>=78)
			       c[k]=3.0*a[k];

	            else 
		            if(b[k]<=77&&b[k]>=75)
		 	           c[k]=2.7*a[k];
	                  else 
	 	                if(b[k]<=74&&b[k]>=72)
		                	c[k]=2.3*a[k];

	                     else 
		                      if(b[k]<=71&&b[k]>=68)
		                     	c[k]=2.0*a[k];

	                            else 
		                           if(b[k]<=67&&b[k]>=64)
			                          c[k]=1.5*a[k];
	                                 else 
		                                 if(b[k]<=63&&b[k]>=60)
			                               c[k]=1.0*a[k];
										 else
											 if(b[k]<60)
												 c[k]=0;
	}
	double q=0,w=0,x;
	int u,v;
	for(u=0;u<n;u++)
	{q=q+c[u];}
	for(v=0;v<n;v++)
	{w=w+a[v];}
	x=q/w;
	printf("%.2lf",x);
	

	return 0;
}

