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: 6



Work Step by Step

The dot plot is roughly bell-shaped, although the sample size is less than 30 (it is 20), hence the sample data is roughly normally distributed, hence $\alpha=1-0.9=0.1.$ $\sigma$ is not known, hence we us the t-distribution with $df=sample \ size-1=20-1=19$ in the table. $t_{\alpha/2}=t_{0.05}=1.729.$
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