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: 79

Answer

20 people: 9.5 minutes 40 people: 39 minutes

Work Step by Step

Each handshake is a selection of 2 people from 20, with no importance in the order. There are ${}_{20}C_{2}=\displaystyle \frac{20\times 19}{1\times 2}=190$ such selections. Each lasting 3 seconds, the total time is: 190$\times$3=570 seconds ( 9.5 minutes) If there were 40 people, the total number of handshakes is: ${}_{20}C_{2}=\displaystyle \frac{40\times 39}{1\times 2}=$780 Total time needed: 780$\times$3= 2340 seconds (39 minutes)
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.