A company has developed a linear trend model to forecast monthly sales. The following data show the actual sales and the "fitted" sales for months 1-12. 
Based on these data, what is the value for the mean absolute deviation for months 1-12?
Definitions:
Miles Per Gallon
A measure of fuel efficiency in vehicles, indicating the distance in miles a vehicle can travel per gallon of fuel consumed.
Simple Random Sample
A segment of a statistical group where every member possesses an identical probability of selection.
Sampling Plan
A strategy that outlines how samples will be collected from a population for the purpose of research or quality control.
Sampling Distribution
The probability distribution of a given statistic based on a random sample, often used to infer about the population.
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