The problem asks for the "simpangan rata-rata" (mean deviation) of the data set $4, 5, 6, 7, 8$.

Steps to calculate the mean deviation:

1. Calculate the mean of the data set: $\text{Mean} = \frac{4 + 5 + 6 + 7 + 8}{5} = \frac{30}{5} = 6$

2. Find the absolute deviations from the mean: $|4 - 6| = 2, \quad |5 - 6| = 1, \quad |6 - 6| = 0, \quad |7 - 6| = 1, \quad |8 - 6| = 2$

3. Calculate the mean of the absolute deviations (mean deviation): $\text{Mean deviation} = \frac{2 + 1 + 0 + 1 + 2}{5} = \frac{6}{5} = 1.2$

So, the mean deviation is 1.2.

Answer: D. $1,2$

Would you like more details or have any questions?

Related Questions:

1. How would the mean deviation change if the data set was $3, 4, 5, 6, 7$?
2. What is the difference between mean deviation and standard deviation?
3. How can you calculate the mean deviation for a larger data set?
4. Why is it necessary to use absolute values when calculating mean deviation?
5. What are the implications of having a high or low mean deviation in a data set?

Tip: Mean deviation is a simple way to measure the variability in a data set. Always ensure to use absolute values to avoid negative deviations canceling out the positive ones.