import heapq

def read_data():
    n = int(input())
    ps = list(map(int, input().split()))
    qs = list(map(int, input().split()))
    return n, ps, qs

def solve(n, ps, qs):
    ps, qs = drop_zero_prob(ps, qs)
    ps = [p / 1000.0 for p in ps]
    qs = [q / 100.0 for q in qs]
    return f(ps, qs)

def drop_zero_prob(ps, qs):
    return zip(*[(p, q) for p, q in zip(ps, qs) if p > 0])
    

def f(ps, qs):
    pqs = [(- p * q, p, 1 - q) for p, q in zip(ps, qs)]
    pqs.sort()
    c = coef = sum_p = 1
    eps = 1.0 * 10**(-5)
    while coef > eps:
        mpq0, p0, qq0 = pqs[0]
        coef *= 1 + mpq0/sum_p
        c += coef
        sum_p += mpq0
        heapq.heapreplace(pqs, (mpq0*qq0, p0*qq0, qq0))
    return c
    

if __name__ == '__main__':
    n, ps, qs = read_data()
    print(solve(n, ps, qs))