Let's calculate the mean and median of the given data set:

The data set is: $9, 2, 19, 21, 39, 15, 0$

Step 1: Sorting the Data Set

To find the median, we need the data in ascending order: $0, 2, 9, 15, 19, 21, 39$

Step 2: Finding the Median

The median is the middle value in a data set when it is ordered. Since there are 7 numbers (an odd number), the median will be the middle number.

• The 4th value in the ordered data set is 15.

So, the median is: $\boxed{15}$

Step 3: Finding the Mean

The mean is the average of all the numbers. To calculate the mean, follow these steps:

1. Add all the numbers together: $9 + 2 + 19 + 21 + 39 + 15 + 0 = 105$
2. Divide the sum by the total number of values (7 in this case): $\frac{105}{7} = 15$

So, the mean is: $\boxed{15}$

Final Results:

• Median: 15
• Mean: 15

Would you like a further explanation or additional questions on this topic? Here are some related questions for you:

1. How do you calculate the median when the data set has an even number of values?
2. What is the difference between mean and median?
3. How do outliers affect the mean and median?
4. What is the mode of a data set, and how does it relate to the mean and median?
5. How would you calculate the range of this data set?

Tip: Always ensure the data set is sorted before finding the median!