#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
 ll MOD=1000000007;
 ll MOD9=998244353;
 int inf=1e9+10;
 ll INF=1e18;
 ll dy[8]={1,0,-1,0,1,1,-1,-1};
 ll dx[8]={0,1,0,-1,1,-1,1,-1};
template <typename T> inline bool chmax(T &a, T b) {
  return ((a < b) ? (a = b, true) : (false));
}
template <typename T> inline bool chmin(T &a, T b) {
  return ((a > b) ? (a = b, true) : (false));
}

int main(){
  ll n;cin >> n;
  vector<double> p(n),q(n);
  rep(i,n)cin >> p[i];
  rep(i,n)cin >> q[i];
  rep(i,n)p[i]/=1000;
  rep(i,n)q[i]/=100;
  double ans=0;
  double now=1;
  ll loop=1000;
  priority_queue<pair<double,int>> que;
  rep(i,n){
    que.push({p[i]*q[i],i});
  }
  for(int loop=1;loop<=1000000;loop++){
    auto v=que.top();que.pop();
    ans+=v.first*loop*now;
    int id=v.se;
    now*=(1.0-v.first)/(p[id]*(1.0-q[id])+(1.0-p[id]));
    p[id]*=(1.0-q[id]);
    que.push({p[id]*q[id],id});
    //cout << ans <<endl;
  }
  CST(10);
  cout << ans <<endl;
}