回复：回复：回复：让人烦恼的礼金卡问题

来源: 于 2009-01-06 21:45:31 [旧帖] [给我悄悄话] 本文已被阅读：次

Why not to find r(1-r)/(1-0.9r)'s max?

which would give r = 1 / (1 + sqrt(10%)).