void main()
{
	int a[10],b[10];
	double c[10];
	double p=0,q=0,pga;
	int n,i;
	scanf("%d",&n);
	for(i=0;i<n;i++)
		scanf("%d",&a[i]);
	for(i=0;i<n;i++)
		scanf("%d",&b[i]);
	for(i=0;i<n;i++)
	{
		if(b[i]>=90)
			c[i]=4.0;
		else if(b[i]>=85)
			c[i]=3.7;
		else if(b[i]>=82)
			c[i]=3.3;
		else if(b[i]>=78)
			c[i]=3.0;
		else if(b[i]>=75)
			c[i]=2.7;
		else if(b[i]>=72)
			c[i]=2.3;
		else if(b[i]>=68)
			c[i]=2.0;
		else if(b[i]>=64)
			c[i]=1.5;
    	else if(b[i]>=60)
			c[i]=1.0;
		else
			c[i]=0;
	}
	for(i=0;i<n;i++)
	{
        q=q+(double)a[i];
		p=p+(double)a[i]*c[i];
	}
	pga=p/q;
	printf("%.2lf",pga);
}