這題PP內沒答案～
但我想知道怎麼解這類題目？
感激！
1. 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?
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Que Pasa
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