The quantity (in pounds) of a gourmet ground coffee that is sold by a coffee company at a price of p dollars per pound is Q = f(p).^1(a) What is the meaning of the derivative f^1(8)? What are its units?
The derivative f'(8) gives the rate of change of the quantity (in pounds) of coffee sold as we increase the price (in dollars).
The units of the derivative are always output units from original function input units from original function . For the original function, the output is pounds of coffee sold, and the input is the price in dollars per pound.
Thus the units for f′(8) are pounds dollars/pound.(b) Is f′(8) positive or negative? Explain. We interpret the rate given by the derivative as the input increases, so the price per pound is increasing. From the law of supply and demand, as the price increases, the quantity sold decreases. Thus we expect
f′(8) to be negative.