Over a 5 week period, the price of an MP3 player dropped steadily, from $140 to $90.

Question

What was the average weekly change in the price of the MP3 player over this period?

Answer 1

That the price "dropped steadily" implies a linear relationship, which would simply be change in price over change in time.

(140 - 90) / 5 = -$10 / week.