#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000000000
	
int main(){	
	
	int n;
	cin>>n;
	
	vector<double> p(n),q(n);
	rep(i,n){
		cin>>p[i];
		p[i] /= 1000.0;
	}
	rep(i,n){
		cin>>q[i];
		q[i] /= 100.0;
	}
	
	priority_queue<pair<double,int>> Q;
	rep(i,n){
		Q.emplace(p[i]*q[i],i);
	}
	
	
	double ans = 0.0;
	double pp = 1.0;
	/*
	double ps = 0.0;
	rep(_,1000000){
		ans += pp;
		auto r = Q.top();
		Q.pop();
		pp *= (1.0 - r.first/ps);
		ps -= r.first;
		r.first *= 1.0 - q[r.second]/ps;
		ps += r.first;
		Q.push(r);
	}
	*/
	rep(_,100000000){
		if(pp<1e-6)break;
		ans += pp;
		int ind = 0;
		rep(i,n){
			if(p[i]*q[i]>p[ind]*q[ind])ind = i;
		}
		
		pp *= 1.0 - p[ind]*q[ind];
		p[ind] *= 1.0-q[ind];
		double ps = 0.0;
		rep(i,n)ps += p[i];
		if(ps<1e-10)break;
		rep(i,n){
			p[i] = p[i] / ps;
		}
	}
	
	cout<<fixed<<setprecision(10)<<ans<<endl;

	return 0;
	
}