Thinking Mathematically (6th Edition)

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

Chapter 11 - Counting Methods and Probability Theory - 11.3 Combinations - Exercise Set 11.3: 16

Answer

12650

Work Step by Step

The number of possible combinations if r items are taken from n items is nCr = $\frac{n!}{r!(n-r)!}$ 25C4 = $\frac{25!}{4!(25 -4)!}$ =$\frac{25!}{4!21!}$ =$\frac{25*24*23*22*21!}{4!21!}$ =$\frac{25*24*23*22}{4*3*2*1} \\= 12650$
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