Error in RocketReview's math?

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1

<p>Hi all,</p>

<p>I was wondering if there is a mistake with RocketReview’s 2005 edition, or if I have been mistaken. The question is on Permutations & Combinations, for those of you who have the book - page 575.</p>

<p>So the book says this: How many different ways can 2 persons finish first and second in a 5 person race?</p>

<p>Ans: 5x4 times 2 (because each “pair” has two different arrangements) = 40</p>

<p>No matter how I look at it, I seem to get 20. Am I doing something wrong?</p>

<p>Thanks in advance!</p>

2

<p>It should be 20. There is an error. We took care of the pairing by considering that EB is different from BE because if you imagine the tree diagram, you’ve taken care of both possibilities, in the original 20.</p>

3

<p>yes the permutation for 5 people taken two at a time is 20.So i guess there must be a mistake in the answer.</p>