Answer
21
Work Step by Step
We know that:
$_nC_r =\frac{_nP_r}{r!} = \frac{n!}{(n-r)!r!}$
$_7C_2 = \frac{7!}{(7-2)!2!}$
$\frac{ 7!}{5!2!}$
We also know that:
$x! = x(x-1)(x-2)...(1)$
Thus, we have:
21
Algebra 1: Common Core (15th Edition)
by Charles, Randall I.
Published by
Prentice Hall
ISBN 10:
0133281140
ISBN 13:
978-0-13328-114-9
Chapter 12 - Data Analysis and Probability - 12-6 Permutations and Combinations - Practice and Problem-Solving Exercises - Page 766: 30
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