import java.util.PriorityQueue;
import java.util.Scanner;

public class Main_yukicoder210 {
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		
		int[] p = new int[n];
		int[] q = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 0; i < n; i++) {
			q[i] = sc.nextInt();
		}

		PriorityQueue<Foo> pq = new PriorityQueue<Foo>();
		for (int i = 0; i < n; i++) {
			pq.add(new Foo((double)p[i] * q[i] / 100000, i));
		}

		double ret = 0.0;
		final double EPS = 1.e-9;
		for (int i = 1; i < 1000000; i++) {
			Foo tmp = pq.poll();
			ret += tmp.p * i;
			tmp.p *= 1.0 - (double)q[tmp.i] / 100;
			if (tmp.p != 0.0 && tmp.p * i < EPS) {
				break;
			}
			pq.add(tmp);
		}
		
		System.out.printf("%.6f\n", ret);
		
		sc.close();
	}

	private static class Foo implements Comparable<Foo> {
		double p;
		int i;

		public Foo(double p, int i) {
			this.p = p;
			this.i = i;
		}

		@Override
		public int compareTo(Foo o) {
			return Double.compare(o.p, this.p);
		}
	}
}