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

ans = 0.0
que = [[-p[i] * q[i], i] for i in xrange(n)]
heapq.heapify(que)
for i in xrange(1, 5000000):
    pq, j = heapq.heappop(que)
    ans += -i * pq / 100000.
    p[j] *= (1 - q[j] / 100.)
    heapq.heappush(que, [-p[j] * q[j], j])
print "%.10f" % ans