※ 引述《william1001 (康)》之铭言： : Tanya prepared 4 different letters to be sent to 4 different addresses. For : each letter, she prepared an envelope with its correct address. If the 4 : letters are to be put into the 4 envelopes at random, what is the probability : that only 1 letter will be put into the envelope with its correct address? : (A) 1/24 : (B) 1/8 : (C) 1/4 : (D) 1/3 : (E) 3/8 : 请问这题怎麽算? 应该有比较快的方法算 不过我用我的笨方法算看看 只放对一个信封的机率 假设第一个放对 其他三个放错 所以机率为(1/4) * (2/3) * (1/2) *1 =1/12 ^^^^^ ^^^^ ^^^^^^^^ 放对 放错 放错 另还有三种可能 :第二个放对 第三个放对 或第四个放对 所以总机率为4*(1/12)=1/3 -- No doubt, just keep walking --

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