Thinking Mathematically (6th Edition)

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

Chapter 2 - Set Theory - 2.1 Basic Set Concepts - Exercise Set 2.1: 115

Answer

$\{20, 21\}$

Work Step by Step

{x | x is a time of the day when 3 $\lt$ average level of happiness $\lt$ 4} From the graph, we can see that this is true only at 20 and 21, because those are the only dots that are strictly between the dotted lines for 3 and 4. Therefore, represented with the roster method, this set looks like this: $\{20, 21\}$
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