void main()
{
	int n=0,i=0;
	int a[10]={0},b[10]={0};
	double c[10]={0},GPA=0,sum_1=0,sum_2=0;
	scanf("%d",&n);
	for(;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]<60)
			c[i]=0;
		if(b[i]>=60&&b[i]<=63)
			c[i]=1;
		if(b[i]>=64&&b[i]<=67)
			c[i]=1.5;
		if(b[i]>=68&&b[i]<=71)
			c[i]=2;
		if(b[i]>=72&&b[i]<=74)
			c[i]=2.3;
		if(b[i]>=75&&b[i]<=77)
			c[i]=2.7;
		if(b[i]>=78&&b[i]<=81)
			c[i]=3;
		if(b[i]>=82&&b[i]<=84)
			c[i]=3.3;
		if(b[i]>=85&&b[i]<=89)
			c[i]=3.7;
		if(b[i]>=90&&b[i]<=100)
			c[i]=4;
	}
	for(i=0;i<n;i++)
		sum_1+=a[i]*c[i];
	for(i=0;i<n;i++)
		sum_2+=a[i];
	GPA=sum_1/sum_2;
	printf("%.2lf",GPA);
}

