Elementary Statistics (12th Edition)

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

Chapter 7 - Estimates and Sample Sizes - 7-4 Estimating a Population Standard Deviation or Variance - Basic Skills and Concepts - Page 369: 7


df=39, $X_{L}^2=24.433$, $ X_{R}^2=59.342$, $\mu$ is between 52.86 and 82.37.

Work Step by Step

$\alpha=1-0.95=0.05.$ By using the table we can find the critical chi-square values with with $df=sample \ size-1=40-1=39$. $X_{L}^2= X_{0.975}^2=24.433$ $ X_{R}^2= X_{0.025}^2=59.342$ Hence the confidence interval:$\mu$ is between $\sqrt{\frac{(n-1)\cdot s^2}{ X_{R}^2}}=\sqrt{\frac{(39)\cdot 65.2^2}{59.342}}=52.86$ and $\sqrt{\frac{(n-1)\cdot s^2}{ X_{L}^2}}=\sqrt{\frac{(39)\cdot 65.2^2}{24.433}}=82.37.$
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