Thinking Mathematically (6th Edition)

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

Chapter 11 - Counting Methods and Probability Theory - 11.2 Permutations - Exercise Set 11.2: 29

Answer

42

Work Step by Step

See Factorial Notation, page 696: $n!=n(n-1)(n-2)\cdots(3)(2)(1)$ and, by definition, $0!=1$ ------------ $\displaystyle \frac{7!}{(7-2)!}=\frac{7!}{5!}=\frac{7\times 6\times 5\times 4\times 3\times 2\times 1}{5\times 4\times 3\times 2\times 1}$ ... reduce $5\times 4\times 3\times 2$ $=7\times 6=42$
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