Answer
1140
Work Step by Step
We know that:
$_nC_r =\frac{_nP_r}{r!} = \frac{n!}{(n-r)!r!}$
$_{20}C_3 = \frac{20!}{(20-3)!3!}$
$\frac{ 20!}{17!3!}$
We also know that:
$x! = x(x-1)(x-2)...(1)$
Thus, we have:
1140
Geometry: Common Core (15th Edition)
by Charles, Randall I.
Published by
Prentice Hall
ISBN 10:
0133281159
ISBN 13:
978-0-13328-115-6
Chapter 13 - Probability - Chapter Review - Page 872: 23
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