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: 2.77a

Answer

Range = $5$ Sample variance = $s^{2}=3.7$ Sample standard deviation = $s =1.924$

Work Step by Step

Recall the shortcut formula for calculating the variance ($s^{2}$)$:$ $$s^{2}=\frac{\sum x_{i}^{2}-\frac{(\sum x_{i})^{2}}{n}}{n-1}$$ Let's create a table in which we compute $\displaystyle \sum x_{i}$ and $\displaystyle \sum x_{i}^{2}$: $$ \begin{array}{rrr} & x & x^{2}\\ \hline & 39 & 1521\\ & 42 & 1764\\ & 40 & 1600\\ & 37 & 1369\\ & 41 & 1681\\\hline \rm Sum & 199 & 7935 \end{array}$$ Plug in the given values (there are $n=5$ data items): $$\begin{align*} s^{2}&= \displaystyle \frac{7935-\frac{(199)^{2}}{5}}{5-1} & & \\ & =3.7 \\\\ s&= \sqrt{3.7} =1.924 \end{align*}$$ The range is the difference between the largest and smallest data item: $42-37=5$
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