Algebra 2 (1st Edition)

Published by McDougal Littell

Chapter 12 Sequences and Series - Cumulative Review - Page 848: 26

21

Work Step by Step

We know the equation for combinations: $$nC_r = \frac{n!}{r!\left(n-r\right)!}$$ Thus, we find: $$\frac{7!}{2!\left(7-2\right)!}=21$$

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