using System;
using System.IO;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;


public class PriorityQueue<T> {
    private T[] array = new T[100];
    private int size = 0;
    private Comparison<T> comp;

    public PriorityQueue() {
        this.comp = Comparer<T>.Default.Compare;
    }

    public PriorityQueue(Comparison<T> comp) {
        this.comp = comp;
    }

    private void Swap(int a, int b) {
        T t = array[a];
        array[a] = array[b];
        array[b] = t;
    }

    private void Expand() {
        var newlist = new T[array.Length * 2];
        Array.Copy(array, newlist, array.Length);
        array = newlist;
    }

    public bool Any() {
        return size > 0;
    }

    public void Enqueue(T newValue) {
        if (size >= array.Length) {
            Expand();
        }
        array[size++] = newValue;
        int pos = size - 1;
        while (pos > 0) {
            int parent = (pos - 1) / 2;
            if (comp(array[parent], array[pos]) > 0) {
                Swap(parent, pos);
                pos = parent;
            } else
                break;
        }
    }

    public T Dequeue() {
        T top = array[0];
        array[0] = array[--size];
        int pos = 0;
        while (pos * 2 + 1 < size) {
            int left = pos * 2 + 1;
            int right = left + 1;
            int next = left;
            if (right < size && comp(array[left], array[right]) > 0)
                next = right;

            if (comp(array[pos], array[next]) > 0) {
                Swap(next, pos);
                pos = next;
            } else
                break;
        }

        return top;
    }
};

public struct Node {
    public double Percentage { get; set; }
    public int Room { get; set; }
}

partial class Solver {
    public void Run() {
        var n = ni();
        var p = ni(n);
        var q = ni(n);

        // メガネがその部屋にある確率
        var percentage = p.Select(x => x / 1000.0).ToArray();
        // 見つかる確率
        var find = q.Select(x => x / 100.0).ToArray();

        var qu = new PriorityQueue<Node>((n1, n2) => -n1.Percentage.CompareTo(n2.Percentage));
        double ans = 0;

        for (int i = 0; i < n; i++) {
            qu.Enqueue(new Node { Percentage = percentage[i] * find[i], Room = i });
        }

        for (int i = 1; i < 1000000; i++) {
            var node = qu.Dequeue();
            ans += i * node.Percentage;
            node.Percentage *= (1.0 - find[node.Room]);
            qu.Enqueue(node);
        }

        cout.WriteLine("{0:F10}", ans);
    }
}

// PREWRITEN CODE BEGINS FROM HERE
partial class Solver : Scanner {
    public static void Main(string[] args) {
        /*new Solver("1 1000 50", Console.Out).Run();
        new Solver(@"10
100 100 100 100 100 100 100 100 100 100
100 100 100 100 100 100 100 100 100 100", Console.Out).Run();
        new Solver(@"10
64 201 4 30 232 64 197 7 102 99
28 43 94 52 24 33 97 55 36 89", Console.Out).Run();*/
        new Solver(Console.In, Console.Out).Run();
    }

    TextReader cin;
    TextWriter cout;

    public Solver(TextReader reader, TextWriter writer)
        : base(reader) {
        this.cin = reader;
        this.cout = writer;
    }
    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer) {
    }

    public int ni() { return NextInt(); }
    public int[] ni(int n) { return NextIntArray(n); }
    public long nl() { return NextLong(); }
    public long[] nl(int n) { return NextLongArray(n); }
    public string ns() { return Next(); }
}

public class Scanner {
    private TextReader Reader;
    private Queue<String> TokenQueue = new Queue<string>();
    private CultureInfo ci = CultureInfo.InvariantCulture;

    public Scanner()
        : this(Console.In) {
    }

    public Scanner(TextReader reader) {
        this.Reader = reader;
    }

    public int NextInt() { return Int32.Parse(Next(), ci); }
    public long NextLong() { return Int64.Parse(Next(), ci); }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size) {
        var array = new string[size];
        for (int i = 0; i < size; i++) array[i] = Next();
        return array;
    }
    public int[] NextIntArray(int size) {
        var array = new int[size];
        for (int i = 0; i < size; i++) array[i] = NextInt();
        return array;
    }

    public long[] NextLongArray(int size) {
        var array = new long[size];
        for (int i = 0; i < size; i++) array[i] = NextLong();
        return array;
    }

    public String Next() {
        if (TokenQueue.Count == 0) {
            if (!StockTokens()) throw new InvalidOperationException();
        }
        return TokenQueue.Dequeue();
    }

    public bool HasNext() {
        if (TokenQueue.Count > 0)
            return true;
        return StockTokens();
    }

    private bool StockTokens() {
        while (true) {
            var line = Reader.ReadLine();
            if (line == null) return false;
            var tokens = line.Trim().Split(" ".ToCharArray(), StringSplitOptions.RemoveEmptyEntries);
            if (tokens.Length == 0) continue;
            foreach (var token in tokens)
                TokenQueue.Enqueue(token);
            return true;
        }
    }
}