Calculate the Variance (sigma²).

The formula for variance for grouped data is:

$$\sigma^2 = \frac{\sum f(x - \bar{x})^2}{\sum f}$$

From the provided table, $\sum f(x - \bar{x})^2 = 2560.32$ and $\sum f = 50$.

Substitute the values into the formula:

$$\sigma^2 = \frac{2560.32}{50}$$ $$\sigma^2 = 51.2064$$

The standard deviation is the square root of the variance:

$$\sigma = \sqrt{\sigma^2}$$

Substitute the calculated variance:

$$\sigma = \sqrt{51.2064}$$ $$\sigma \approx 7.156$$

The variance is $\boxed{51.2064}$
The standard deviation is $\boxed{7.156}$