Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

Published by Pearson
ISBN 10: 0-32193-104-1
ISBN 13: 978-0-32193-104-7

Chapter 12 - Counting and Probability - Section 12.2 Permutations and Combinations - 12.2 Assess Your Understanding - Page 875: 31


$16$ two-letter codes

Work Step by Step

The first letter can be A,B,C or D. So there are 4 choices for the first. Similarly, the second letter can also be A,B,C or D as repetition is allowed. According to multiplication principle, Number of 2-letter codes = $4\times4 = 16$
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