To determine the median of the given numbers:

Steps:

1. List the numbers in ascending order:
   Original list: $13, 8, 17, 12, 4, 15$
   Sorted list: $4, 8, 12, 13, 15, 17$

2. Count the total number of elements:
   There are $6$ numbers.

3. Find the middle value(s):
   Since there are an even number of elements, the median is the average of the two middle numbers.
   Middle numbers: $12$ and $13$.

4. Calculate the median:
   $\text{Median} = \frac{12 + 13}{2} = 12.5$

Final Answer:

The median of these numbers is 12.5.

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Related Questions:

1. How do you calculate the median if the number of elements is odd?
2. What is the difference between median, mean, and mode?
3. How does the median change if you add another number to the list?
4. Can the median be a decimal when all the numbers are integers?
5. How is the median used in real-life statistical analysis?

Tip:

When finding the median, always ensure the numbers are properly sorted in ascending order before identifying the middle value(s).