Essentials of Statistics (5th Edition)

Published by Pearson
ISBN 10: 0-32192-459-2
ISBN 13: 978-0-32192-459-9

Chapter 7 - Estimates and Sample Sizes - 7-3 Estimating a Population Mean - Page 350: 8



Work Step by Step

Although the dot plot is not roughly bell-shaped, the sample size is more than 30 (it is 40), hence the sample data is roughly normally distributed, hence $\alpha=1-0.99=0.01.$ $\sigma$ is known, hence we use the z-distribution with the table. $z_{\alpha/2}=z_{0.05}=2.575.$
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