The quantity q of beef purchased at a store in kilograms

Question

Question: The quantity, Q, of beef purchased at a store, in kilograms per week, is a function of the price of beef, b, and the price of chicken, c, both in dollars per kilogram.

(a) Do you expect ∂Q/∂b to be positive or negative? Explain.

(b) Do you expect ∂Q/∂c to be positive or negative? Explain.

(c) Interpret the statement ∂Q/∂b = -213 in terms of quantity of beef purchased.