回複：回複：回複：讓人煩惱的禮金卡問題

來源: justatry 於 2009-01-06 21:45:31 [] [舊帖] [給我悄悄話] 閱讀數 : (88 bytes)
回答: 回複：讓人煩惱的禮金卡問題 由 justatry 於 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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