Geometry: Common Core (15th Edition)

Published by Prentice Hall
ISBN 10: 0133281159
ISBN 13: 978-0-13328-115-6

Chapter 13 - Probability - Chapter Review - Page 872: 21



Work Step by Step

$_{10}$P$_{2}$ is a permutation. To solve, use the permutation formula: $_{n}$P$_{r}$ = $\frac{n!}{(n-r)!}$ Plug in 10 for "n" and 2 for "r": $_{n}$P$_{r}$ = $\frac{n!}{(n-r)!}$ $_{10}$P$_{2}$ = $\frac{10!}{(10-2)!}$ = $\frac{10!}{8!}$ = $\frac{10\times9\times8\times7\times6\times5\times4\times3\times2\times1}{8\times7\times6\times5\times4\times3\times2\times1}$ As 8x7x6x5x4x3x2x1 appears in both the numerator and denominator, we can cancel out these numbers. We are then left with: 10 x 9 = 90
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