Statistics (12th Edition)

Published by Pearson
ISBN 10: 0321755936
ISBN 13: 978-0-32175-593-3

Chapter 2 - Methods for Describing Sets of Data - Exercises 2.71 - 2.89 - Learning the Mechanics - Page 64: 2.82b

Answer

Sample variance = $s^{2}=152.25\text{ sq. feet}$ Sample standard deviation = $s =12.34\text{ feet}$

Work Step by Step

Recall the shortcut formula for calculating the variance ($s^{2}$)$:$ $$s^{2}=\frac{\sum x_{i}^{2}-\frac{(\sum x_{i})^{2}}{n}}{n-1}$$ Create a table in which we compute $\displaystyle \sum x_{i}$ and $\displaystyle \sum x_{i}^{2}.$ $$ \begin{array}{rrr} & x & x^{2}\\ \hline & 8 & 64\\ & 10 & 100\\ & 32 & 1024\\ & 5 & 25\\ \hline\rm Sum & 55 & 1213 \end{array}$$ Plug in the given values (there are $n=4$ data items). $$\begin{align*} s^{2}&= \displaystyle \frac{1213-\frac{(55)^{2}}{4}}{41} & & \\ & =152.25\text{ sq. feet} \\\\ s&= \sqrt{11.4} =12.34\text{ feet} \end{align*}$$
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