n = gets.to_i
p = gets.split.map(&:to_i)
q = gets.split.map(&:to_i)
r = p.map {|x| x / 1000.0}
s = 1.0
ans = 0
1.upto(10**4) do |k|
  z = r.zip(q).map {|x, y| x*y}
  m, i = z.each_with_index.max
  ans += k * s * (m / 100.0)
  s *= 1 - m / 100.0
  d = 1 - r[i] * q[i] / 100.0
  r.each_with_index do |e, j|
    r[j] = if j == i
             r[j] * (1 - q[j] / 100.0) / d
           else
             r[j] / d
           end
  end
end
puts ans