n = int(raw_input())
p = map(int, raw_input().split())
q = map(int, raw_input().split())

ans = 0.0
for i in xrange(1, 10000):
    pq = [p[j] * q[j] / 1000. /100. for j in xrange(n)]
    j = pq.index(max(pq))
    ans += i * pq[j]
    p[j] *= (1 - q[j] / 100.)
print "%.10f" % ans