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]
    eps = 1.0/(1000 * 10000)
    return f(ps, qs, eps)

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

def f(ps, qs, eps):
    c = 1
    pqs = [p * q for p, q in zip(ps, qs)]
    coef = 1
    while coef > eps:
        sum_p = sum(ps)
        max_pq = max(pqs)
        i = pqs.index(max_pq)
        p = 1 - qs[i]
        ps[i] *= p
        pqs[i] *= p
        coef *= 1 - max_pq/sum_p
        c += coef
    return c
    

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