1. **State the problem:** Find the average of the list of numbers: -15, 3, -8, 7, -9, 2, -1. 2. **Formula for average:** The average (mean) of a list of numbers is given by $$\text{Average} = \frac{\text{Sum of all numbers}}{\text{Number of numbers}}$$ 3. **Calculate the sum:** $$-15 + 3 + (-8) + 7 + (-9) + 2 + (-1) = -15 + 3 - 8 + 7 - 9 + 2 - 1$$ Calculate step-by-step: $$-15 + 3 = -12$$ $$-12 - 8 = -20$$ $$-20 + 7 = -13$$ $$-13 - 9 = -22$$ $$-22 + 2 = -20$$ $$-20 - 1 = -21$$ So, the sum is $$-21$$. 4. **Count the numbers:** There are 7 numbers in the list. 5. **Calculate the average:** $$\text{Average} = \frac{-21}{7}$$ Show cancellation: $$\frac{\cancel{-21}}{\cancel{7}} = -3$$ 6. **Final answer:** The average of the list is **-3**. **Answer:** -3