float GPA(int n)
{
	int i;
	float result;
	float gpa[10];
	float gpa_1[10];
	float sumxf=0;
	float sumcj=0;
	int chengji[10],xuefen[10];
	for(i=0;i<n;i++)
		scanf("%d",&xuefen[i]);
	for(i=0;i<n;i++)
		scanf("%d",&chengji[i]);
	for(i=0;i<n;i++)
	{
		if(90<=chengji[i]&&chengji[i]<=100)gpa[i]=4.0;
		else if(85<=chengji[i]&&chengji[i]<=89)gpa[i]=3.7;
		else if(82<=chengji[i]&&chengji[i]<=84)gpa[i]=3.3;
		else if(78<=chengji[i]&&chengji[i]<=81)gpa[i]=3.0;
		else if(75<=chengji[i]&&chengji[i]<=77)gpa[i]=2.7;
		else if(72<=chengji[i]&&chengji[i]<=74)gpa[i]=2.3;
		else if(68<=chengji[i]&&chengji[i]<=71)gpa[i]=2.0;
		else if(64<=chengji[i]&&chengji[i]<=67)gpa[i]=1.5;
		else if(60<=chengji[i]&&chengji[i]<=63)gpa[i]=1.0;
		else gpa[i]=0;
	}
	for(i=0;i<n;i++)
	{
	gpa_1[i]=gpa[i]*xuefen[i];
	sumcj+=gpa_1[i];
	sumxf+=xuefen[i];
	}
	result=sumcj/sumxf;
	return result;
}
void main()
{
	int n;
	float gpa; 
	scanf("%d",&n);
	gpa=GPA(n);
	printf("%.2f",gpa);
}
