An Operation Analyst Is Forecasting This Year's Demand for One

Multiple Choice

An operation analyst is forecasting this year's demand for one of his company's products based on the following historical data:
$$\begin{array} { | c | c | } \hline \text { Year } & \text { \# Sald } \\\hline 4 \text { years ago } & 10,000 \\\hline 3 \text { years ago } & 12,000 \\\hline \text { 2 years ago } & 18,000 \\\hline \text { Last year } & 20,000 \\\hline\end{array}$$
The previous trend line has predicted 18,500 for two years ago, and 19,700 for last year. What was the mean absolute deviation for these forecasts?

A) 100
B) 200
C) 400
D) 500
E) 800