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: 2.81c

Answer

Range =$3$ Sample variance = $s^{2}=1.3$ Sample standard deviation = $s =1.14$

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 $\displaystyle \sum x_{i}^{2}.$ Recall that we subtract 4 from all the data items given in the problem text. $$ \begin{array}{lll} & x & x^{2}\\ \hline & -2 & 4\\ & -3 & 9\\ & -3 & 9\\ & -4 & 16\\ & -1 & 1\\ \hline\rm Sum & -13 & 39 \end{array}$$ Plug in the given values (there are $n=5$ data items): $$\begin{align*} s^{2}&= \displaystyle \frac{39-\frac{(-13)^{2}}{5}}{5-1} & & \\ & =1.3 \\\\ s&= \sqrt{1.3} =1.14 \end{align*}$$ The range is the difference between the largest and smallest data item: $-1-(-4)=3$
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