int main ()
{
	int n;
	int sumxuefen = 0;
	int i;
	float sumjidian = 0;
	float sumxuefenjidian = 0;
	float GPA;	
	int xuefen[10];
	int scores[10];
	float jidian[10];
	float xuefenjidian[10];
	scanf("%d", &n);
	for(i=0;i<n;i++){
		scanf("%d", &xuefen[i]);
		sumxuefen = sumxuefen + xuefen[i];
	}
	for(i=0;i<n;i++){
		scanf("%d",&scores[i]);
		if(scores[i]==100||scores[i]==99||scores[i]==98||scores[i]==97||scores[i]==96||scores[i]==95||scores[i]==94||scores[i]==93||scores[i]==92||scores[i]==91||scores[i]==90){
			jidian[i] = 4.0;
		}
		else if(scores[i]==89||scores[i]==88||scores[i]==87||scores[i]==86||scores[i]==85){
			jidian[i] = 3.7;
		}
		else if(scores[i]==84||scores[i]==83||scores[i]==82){
			jidian[i] = 3.3;
		}
		else if(scores[i]==81||scores[i]==80||scores[i]==79||scores[i]==78){
			jidian[i] = 3.0;
		}
		else if(scores[i]==77||scores[i]==76||scores[i]==75){
			jidian[i] = 2.7;
		}
		else if(scores[i]==74||scores[i]==73||scores[i]==72){
			jidian[i] = 2.3;
		}
		else if(scores[i]==71||scores[i]==70||scores[i]==69||scores[i]==68){
			jidian[i] = 2.0;
		}
		else if(scores[i]==67||scores[i]==77||scores[i]==65||scores[i]==64){
			jidian[i] = 1.5;
		}
		else if(scores[i]==63||scores[i]==62||scores[i]==61||scores[i]==60){
			jidian[i] = 2.0;
		}
		else {
			jidian[i] = 0;
		}
			sumjidian = sumjidian + jidian[i];
	}
	for(i=0;i<n;i++){
	    xuefenjidian[i] = jidian[i] * xuefen[i];
	}
  for(i=0;i<n;i++){
	  sumxuefenjidian = sumxuefenjidian + xuefenjidian[i];
  }
		GPA = sumxuefenjidian * 1.00/sumxuefen;
		printf("%.2f", GPA);
		return 0;
	}
		