1. **State the problem:** Find the interquartile range (IQR) of the data set: 8, 4, 7, 6, 15, 12, 16, 18. 2. **Sort the data:** Arrange the numbers in ascending order: 4, 6, 7, 8, 12, 15, 16, 18. 3. **Find the quartiles:** - The median (Q2) splits the data into two halves. Since there are 8 numbers (even), median is average of 4th and 5th values: $$Q2 = \frac{8 + 12}{2} = 10$$ - Lower half: 4, 6, 7, 8. Median of this is Q1: $$Q1 = \frac{6 + 7}{2} = 6.5$$ - Upper half: 12, 15, 16, 18. Median of this is Q3: $$Q3 = \frac{15 + 16}{2} = 15.5$$ 4. **Calculate the interquartile range:** $$IQR = Q3 - Q1 = 15.5 - 6.5 = 9$$ 5. **Interpretation:** The interquartile range is 9, which measures the spread of the middle 50% of the data.