#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

int main() {
	int n;
	scanf("%d", &n);
	vector<int> p(n), q(n);
	rep(i, n) {
//		p[i]=1;
		scanf("%d", &p[i]);
	}
	rep(i, n) {
//		q[i]=1;
		scanf("%d", &q[i]);
	}
	vector<double> prob(n);
	int sum = accumulate(all(p), 0);
	rep(i, n) prob[i] = p[i] * 1. / sum;
	priority_queue<pair<double,int> > pq;
	rep(i, n) pq.push(mp(prob[i] * q[i], i));
	double ans = 0, remprob = 1, mult = 1;
	while(remprob > 0.000025) {
		//sum prob = 1
		//prob[i] = iにある確率
		pair<double,int> a = pq.top(); pq.pop();
		int i = a.second;
		double x = prob[i] / mult, y = q[i] / 100.;
		double sum = 1 - prob[i] / mult;
		ans += remprob;
		double z = (1-x) + x * (1-y);	//見つからない確率
		remprob *= z;
		double w = 1 - (1-x) / z;	//見つからないときにある
//		cerr << ans << ", " << remprob << ", " << i << ", " << x << ", " << y << ", " << z << ", " << w << endl;
		double nsum = 1 - w;
		if(nsum > 0) mult *= sum / nsum;
		prob[i] = w * mult;
		pq.push(mp(prob[i] * q[i], i));
	}
	printf("%.10f\n", ans);
	return 0;
}