Comments of ext_1788645 (1)
Comment on post Adventures in math: finding a red dot in a book, Marilyn vos Savant is wrong!:
Greg is correct.
Let's say you read 90% of the pages. You're saying there is a 90% chance the red dot is on one of the remaining pages. And, when you read all but the last page, there is a 90% chance it will be on the last page.
The logic flaw is that you do, in fact, learn something about the location of the red dot when you read half the book and don't find it. It's not like the Monty Hall problem, where you really don't learn anything about your choice when the goat is revealed.
Greg is correct that you should assume a 45% chance the dot is in each half of the book. When you find no dot in the first half of the book, there is a .45/.55 probability in the last half of the book.
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