Elementary Statistics (12th Edition)

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

Chapter 7 - Estimates and Sample Sizes - 7-2 Estimating a Population Proportion - Basic Skills and Concepts - Page 337: 6



Work Step by Step

$\alpha=1-confidence \ level=1-99$%$=1-0.99=0.01.$ Hence $1-\frac{\alpha}{2}=1-0.005=0.995.$ $z_{\frac{\alpha}{2}}$ is the z score belonging to the probability of $1-\frac{\alpha}{2}=0.995$, which is 2.575.
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