Q&A

To correct for overcounting, why can't we divide by the sum of the over-counts? [duplicate]

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Closed as duplicate by Peter Taylor‭ on Jan 24, 2022 at 08:52

This question has been addressed elsewhere. See: Why 1. multiply the number of independent options? 2. add the number of exclusive options?

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The book doesn't expatiate the sentence underlined in red below. 1. Why "it isn't 2 + 2"?

1. Note that $2 \times 2 = 2 + 2 = 4$! Is this a coincidence?

Problem 3.4: How many distinct arrangements are there of PAPA?

David Patrick, BS Math & Computer Science, MS Math (Carnegie Mellon), PhD Math (MIT). Introduction to Counting & Probability (2005), p 50.

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