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: 9


σ is between 0.57 and 0.72.

Work Step by Step

$\alpha=1-0.9=0.1.$ By using the table we can find the critical chi-square values with with $df=sample \ size-1=106-1=105$. $X_{L}^2= X_{0.975}^2=77.929$ $ X_{R}^2= X_{0.025}^2=124.342$ Hence the confidence interval:$\sigma$ is between $\sqrt{\frac{(n-1)\cdot s^2}{ X_{R}^2}}=\sqrt{\frac{(105)\cdot 0.62^2}{124.342}}=0.57$ and $\sqrt{\frac{(n-1)\cdot s^2}{ X_{L}^2}}=\sqrt{\frac{(105)\cdot 0.62^2}{77.929}}=0.72.$
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