Answer
Sample variance = $s^{2}=4.8889$
Sample standard deviation = $s =2.21$
Work Step by Step
Recall the shortcut formula for calculating the variance ($s^{2}$):
$$s^{2}=\frac{\sum_{i=1}^{n}x_{i}^{2}-\dfrac{\left(\sum_{i=1}^{n}x_{i}\right)^{2}}{n}}{n-1}$$
Plug in the given values:
$$\begin{align*}
s^{2}&= \displaystyle \frac{84-\frac{\left(20\right)^{2}}{10}}{10-1} & & \\
& =4.8889 \\\\
s&= \sqrt{4.8889} =2.21 \end{align*}$$
