Find the range, inter quartile range and semi-inter quartile range of the following data.

The given data points are: 9, 21, 49, 10, 40, 51, 28, 37, 18, 21, 22, 8, 30, 34, 12, 45, 43, 9, 31, 12.
Rearranging the data in ascending order:

$$8, 9, 9, 10, 12, 12, 18, 21, 21, 22, 28, 30, 31, 34, 37, 40, 43, 45, 49, 50$$

The number of data points is $n = 20$.

The range is the difference between the maximum and minimum values in the dataset.
Maximum value = 50
Minimum value = 8

$$\text{Range} = \text{Maximum value} - \text{Minimum value} = 50 - 8 = \boxed{\text{42}}$$

The position of the lower quartile (Q1) is given by the formula $\frac{1}{4}(n+1)^{\text{th}}$.

$$\text{Q1 position} = \frac{1}{4}(20+1)^{\text{th}} = \frac{1}{4}(21)^{\text{th}} = 5.25^{\text{th}}$$

This means Q1 is between the 5th and 6th values.
The 5th value in the sorted data is 12.
The 6th value in the sorted data is 12.

$$\text{Q1} = \text{5th value} + 0.25 \times (\text{6th value} - \text{5th value})$$ $$\text{Q1} = 12 + 0.25 \times (12 - 12) = 12 + 0.25 \times 0 = 12$$

The position of the upper quartile (Q3) is given by the formula $\frac{3}{4}(n+1)^{\text{th}}$.

$$\text{Q3 position} = \frac{3}{4}(20+1)^{\text{th}} = \frac{3}{4}(21)^{\text{th}} = 15.75^{\text{th}}$$

This means Q3 is between the 15th and 16th values.
The 15th value in the sorted data is 37.
The 16th value in the sorted data is 40.

$$\text{Q3} = \text{15th value} + 0.75 \times (\text{16th value} - \text{15th value})$$ $$\text{Q3} = 37 + 0.75 \times (40 - 37) = 37 + 0.75 \times 3 = 37 + 2.25 = 39.25$$

The interquartile range is the difference between the upper quartile (Q3) and the lower quartile (Q1).

$$\text{IQR} = \text{Q3} - \text{Q1} = 39.25 - 12 = \boxed{\text{27.25}}$$

The semi-interquartile range is half of the interquartile range.

$$\text{SIQR} = \frac{\text{IQR}}{2} = \frac{27.25}{2} = \boxed{\text{13.625}}$$