The frequency distribution is given below:
$\begin{array}{|l|l|l|l|l|l|l|} \hline X & 2 & 3 & 4 & 5 & 6 & 7 \\ f & 4 & 9 & 16 & 14 & 11 & 6 \\ \hline \end{array}$
Find the standard deviation.

(D) First,we calculate the mean $\bar{x} = \frac{\sum f_i x_i}{\sum f_i} = \frac{(2 \times 4) + (3 \times 9) + (4 \times 16) + (5 \times 14) + (6 \times 11) + (7 \times 6)}{4 + 9 + 16 + 14 + 11 + 6} = \frac{8 + 27 + 64 + 70 + 66 + 42}{60} = \frac{277}{60} \approx 4.6167$.
Using the formula for standard deviation $\sigma = \sqrt{\frac{\sum f_i x_i^2}{N} - \bar{x}^2}$:
$\sum f_i x_i^2 = (4 \times 4) + (9 \times 9) + (16 \times 16) + (14 \times 25) + (11 \times 36) + (6 \times 49) = 16 + 81 + 256 + 350 + 396 + 294 = 1393$.
$\sigma = \sqrt{\frac{1393}{60} - (4.6167)^2} = \sqrt{23.2167 - 21.3139} = \sqrt{1.9028} \approx 1.38$.