Thinking Mathematically (6th Edition)

Published by Pearson
ISBN 10: 0321867327
ISBN 13: 978-0-32186-732-2

Chapter 11 - Counting Methods and Probability Theory - 11.3 Combinations - Exercise Set 11.3 - Page 709: 73


Does not make sense.

Work Step by Step

A password implies the importance of order of the letters. For example, "wand" and "dawn" are different orderings of the same four letters and make two different passwords. Order is important. Permutations should be used, not combinations. The formula for ${}_{n}P_{r}$ should be used.
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