To find the relative frequency of 13 in the given data set, follow these steps:

1. Identify the total number of data points: The data set is: 13, 18, 12, 4, 3.
   Total number of data points = 5.

2. Count how many times 13 appears: The number 13 appears once.

3. Calculate the relative frequency: The formula for relative frequency is: $\text{Relative Frequency} = \frac{\text{Frequency of the value}}{\text{Total number of data points}}$ Substituting the values: $\text{Relative Frequency of 13} = \frac{1}{5} = 0.2$

Thus, the relative frequency of 13 is 0.2 (or 20%).

Would you like any more details or explanations on this?

Here are some related questions:

1. What is the relative frequency of other numbers in the dataset?
2. How is relative frequency different from absolute frequency?
3. Can relative frequencies be expressed as percentages?
4. What happens if a number appears multiple times in the data set?
5. How do you calculate cumulative relative frequency?

Tip: The sum of all relative frequencies in a dataset should always equal 1 (or 100% when expressed as a percentage).