回复：回复：回复：让人烦恼的礼金卡问题

来源: justatry 于 2009-01-06 21:45:31 [] [旧帖] [给我悄悄话] 阅读数 : (88 bytes)
回答: 回复：让人烦恼的礼金卡问题 由 justatry 于 2009-01-02 21:31:57

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

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

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