import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] arr = new int[n];
        for (int i = 0; i < n; i++) {
            arr[i] = sc.nextInt();
        }
        PriorityQueue<Room> queue = new PriorityQueue<>();
        for (int i = 0; i < n; i++) {
            queue.add(new Room(arr[i], sc.nextInt()));
        }
        double expect = 0;
        for (int i = 1; i < 10000000; i++) {
            Room r = queue.poll();
            expect += r.allRate * i;
            r.next();
            queue.add(r);
        }
        System.out.println(expect);
    }
    
    static class Room implements Comparable<Room> {
        double rate;
        double allRate;
        
        public Room (int rate1, int rate2) {
            rate = rate2 / 100.0;
            allRate = rate1 / 1000.0 * rate;
            rate = 1 - rate;
        }
        
        public int compareTo(Room another) {
            if (allRate == another.allRate) {
                return 0;
            } else if (allRate > another.allRate) {
                return -1;
            } else {
                return 1;
            }
        }
        
        public void next() {
            allRate *= rate;
        }
    }
}