Elementary Statistics (12th Edition)

Published by Pearson
ISBN 10: 0321836960
ISBN 13: 978-0-32183-696-0

Chapter 7 - Estimates and Sample Sizes - 7-3 Estimating a Population Mean - Basic Skills and Concepts - Page 359: 25


68, which seems to be fine.

Work Step by Step

$\alpha=1-0.9=0.1.$ Using the table: $z_{\alpha/2}=z_{0.05}=1.645.$ Hence the sample size:$\left (\frac{z_{\alpha/2}\cdot \sigma}{E}\right)^2=\left (\frac{1.645\cdot 15}{3}\right)=68$, which seems to be fine.
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