/*
    GPA计算
    学生成绩实行平均学分绩点制
        实际考分按照不同的学科的不同学分按一定的公式进行计算
            分段
                90-100    4.0
                85-89    3.7
                82-84    3.3
                78-81    3
                75-77    2.7
                72-74    2.3
                68-71    2
                64-67    1.5
                60-63    1
                60以下    0
            公式：
                1、一门课程的学分绩点=该课绩点*该课学分
                2、总评绩点=所有学科绩点之和/所有课程学分之和
                
            分析：输入总的课程数n（n<10）
                 相应课程得到的学分（空格隔开）
                 对应的实际得分
                 
             得到了我们需要的条件 
             然后开始计算我们的gpa
*/

import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner in=new Scanner(System.in);
        int n=in.nextInt();
        int gradePoint[]=new int[n];//每门课学分
        int coursePoint[]=new int[n];//每门课分数
         
        for(int i=0;i<n;i++){
            gradePoint[i]=in.nextInt();
        }
        for(int i=0;i<n;i++){
            coursePoint[i]=in.nextInt();
        }
        in.close();
        System.out.printf("%.2f",gradePointAverage(gradePoint,coursePoint));//格式输出
         
    }
    public static double pointOfEachCourse(int grade){//根据实际成绩判断学分方法
        double point = 0.0;
        if(grade>=90&&grade<=100)
            point=4.0;
         
        if(grade>=85&&grade<=89)
            point=3.7;
         
        if(grade>=82&&grade<=84)
            point=3.3;
         
        if(grade>=78&&grade<=81)
            point=3.0;
         
        if(grade>=75&&grade<=77)
            point=2.7;
         
        if(grade>=72&&grade<=74)
            point=2.3;
         
        if(grade>=68&&grade<=71)
            point=2.0;
         
        if(grade>=64&&grade<=67)
            point=1.5;
         
        if(grade>=60&&grade<=63)
            point=1.0;
         
        if(grade<60)
            point=0.0;
         
        return (double)point;
    }
    //计算平均绩点的方法
    public static double gradePointAverage(int[] gradePoint,int[] coursePoint){
        double gradePointTotal=0;
        double gradeOfEachCourseTotal=0;
        for(int i=0;i<gradePoint.length;i++){
            gradePointTotal+=pointOfEachCourse(coursePoint[i])*gradePoint[i];
            gradeOfEachCourseTotal+=gradePoint[i];
        }
        return (double)gradePointTotal/gradeOfEachCourseTotal;
    }
}