#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (ll i=(ll)from; i<(ll)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (int i=(int)N-1; i>=0; i--)

const ll MOD = pow(10,9)+7;
const ll LLINF = pow(2,61)-1;
const int INF = pow(2,30)-1;

vector<ll> fac;
void c_fac(int x=pow(10,6)+10) { fac.resize(x,true); rep(i,x) fac[i] = i ? (fac[i-1]*i)%MOD : 1; }
ll inv(ll a, ll m=MOD) { ll b = m, x = 1, y = 0; while (b!=0) { int d = a/b; a -= b*d; swap(a,b); x -= y*d; swap(x,y); } return (x+m)%m; }
ll nck(ll n, ll k) { return fac[n]*inv(fac[k]*fac[n-k]%MOD)%MOD; }
ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }

struct room {
  double p, q;
  bool operator> (const room &x) const { return p*q>x.p*x.q||(p*q==x.p*x.q&&p>x.p); };
  bool operator< (const room &x) const { return p*q<x.p*x.q||(p*q==x.p*x.q&&p<x.p); };
};

int main() {
  ll n; cin >> n; 
  double p[n]; rep(i,n) { cin >> p[i]; p[i]/=1000; }
  double q[n]; rep(i,n) { cin >> q[i]; q[i]/=100; }
  priority_queue<room> pq; rep(i,n) pq.push({p[i],q[i]});

  double result = 0, np = 1, nall = 1;
  rep(i,1000000) { 
    room now = pq.top(); pq.pop();
    // cout << np << " " << now.q << " " << result << endl;
    result += (i+1) * now.p * np / nall * now.q;
    np -= now.p*now.q; nall -= now.p * now.q; now.p -= now.p * now.q;
    pq.push(now);
  }

  cout << setprecision(10) << result << endl;
  return 0;
}