Answer
Range =$24$
Sample variance = $s^{2}=72.7$
Sample standard deviation = $s = 8.526$
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 of the number of books read by students marked with a $B$ or $C$, with which we compute $\displaystyle \sum x_{i}$ and $\displaystyle \sum x_{i}^{2}$:
$$ \begin{array}{lll}
x & \rm Grade & x^{2}\\
\hline 40 & \mathrm{B} & 1600\\
28 & \mathrm{B} & 784\\
22 & \mathrm{C} & 484\\
21 & \mathrm{B} & 441\\
20 & \mathrm{B} & 400\\
16 & \mathrm{B} & 256\\
& & \\
\hline\rm Sum=147 & & 3965
\end{array}$$
Plug in the given values (there are $n=8$ data items):
$$\begin{align*}
s^{2}&= \displaystyle \frac{3965-\frac{(147)^{2}}{5}}{5-1} & & \\
& =72.7\\\\
s&= \sqrt{72.7} =8.526 \end{align*}$$
The range is the difference between the largest and smallest data item:
$$40-16=24$$
