Final answer:
The Mean Absolute Deviation (MAD) for the forecast errors of -5, -10, and +15 is calculated by taking the mean of the absolute values of these errors, resulting in a MAD of 10.
Step-by-step explanation:
The Mean Absolute Deviation (MAD) is a measure used to find out how spread out numbers are in a data set. To calculate MAD, you first need to find the absolute values of the forecast errors. Given the forecast errors of -5, -10, and +15, we calculate the absolute values, which are 5, 10, and 15, respectively.
Next, we find the mean of these absolute values:
(5 + 10 + 15) / 3 = 30 / 3 = 10.
Therefore, the MAD for the forecast errors given is 10.