Elementary Statistics: A Step-by-Step Approach with Formula Card 9th Edition

Published by McGraw-Hill Education
ISBN 10: 0078136334
ISBN 13: 978-0-07813-633-7

Chapter 7 - Confidence Intervals and Sample - 7-3 Confidence Intervals and Sample Size for Proportions - Exercises 7-3 - Page 396: 9

Answer

$0.596\lt p\lt0.704$

Work Step by Step

We have $\hat p=\frac{195}{300}=0.65, \hat q=1-\hat p=0.35 , n=300 $ At a 95% confidence the critical z-value is $z_{\alpha/2}=1.96 $ The margin of error can be found as $E=z_{\alpha/2}\times\sqrt {\frac{\hat p\hat q}{n}}=1.96\times\sqrt {\frac{0.65\times0.35}{300}}=0.054$ Thus, the interval of the true proportion can be found as $\hat p-E\lt p\lt\hat p+E$ which gives $0.596\lt p\lt0.704$
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