
void main(){
	double c[10], s[10], p[10], tc=0, tp=0, GPA;
	int i, n;
	scanf("%d", &n);
	for (i=0; i<n; i++)
	{
		scanf("%lf", &c[i]);
		tc=tc+c[i];
	}
	for (i=0; i<n; i++)
	{
		scanf("%lf", &s[i]);
		if (s[i]<60) p[i]=0;
		else if (s[i]>=60 && s[i]<=63) p[i]=1.0*c[i];
		else if (s[i]>=64 && s[i]<=67) p[i]=1.5*c[i];
		else if (s[i]>=68 && s[i]<=71) p[i]=2.0*c[i];
		else if (s[i]>=72 && s[i]<=74) p[i]=2.3*c[i];
		else if (s[i]>=75 && s[i]<=77) p[i]=2.7*c[i];
		else if (s[i]>=78 && s[i]<=81) p[i]=3.0*c[i];
		else if (s[i]>=82 && s[i]<=84) p[i]=3.3*c[i];
		else if (s[i]>=85 && s[i]<=89) p[i]=3.7*c[i];
		else p[i]=4.0*c[i];
		tp=tp+p[i];
	}
	GPA=tp/tc;
	printf("%.2lf", GPA);
}