#include<iostream>
#include<fstream>
#include<sstream>
#include<string>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<stack>
#include<queue>
#include<set>
#include<map>
#include<vector>
#include<list>
#include<algorithm>
#include<utility>
#include<complex>
#include<functional>
using namespace std;
const double eps = 1e-7;

int main(void){
	int n;
	double p[1000], q[1000];
	double Q[1000];
	cin >> n;
	for (int i = 0; i < n; i++){
		cin >> p[i];
		p[i] /= 1000;
	}
	for (int i = 0; i < n; i++){
		cin >> q[i];
		Q[i] = 1;
		q[i] /= 100;
	}
	double E = 0;
	int cnt = 0;
	while (1){
		cnt ++;
		int index = 0;
		double px = 0;
		for (int i = 0; i < n; i++){
			double d = p[i] * q[i] * Q[i];
			if (d > px){
				index = i;
				px = d;
			}

		}
		E += cnt*px;
		Q[index] *= (1 - q[index]);
		if (cnt*px < eps)break;
	}
	printf("%.4f\n", E);

	return(0);
}