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Problems 91–94 refer to the following: If a decrease in demand for one product results in an increase in demand for another product, the two products are said to be competitive, or substitute,
products. (Real whipping cream and imitation whipping cream are examples of competitive, or substitute, products.) If a decrease in demand for one product results in a decrease in demand for another product, the two products are said to be complementary products. (Fishing boats and outboard motors are examples of complementary products.) Partial derivatives can be used to test whether two products are competitive, complementary, or neither. We start with demand functions for two products such that the demand for either depends on the prices for both:
The variables x and y represent the number of units demanded of products A and B, respectively, at a price p for 1 unit of product A and a price q for I unit of product B. Normally, if the price of A increases while the price of B is held constant, then the demand for A will decrease; that is, fp(p, q) < 0. Then, if A and B are competitive products, the demand for B will increase; that is, gr(p, q) > 0. Similarly, if the price of B increases while the price of A is held constant, the demand for B will decrease; that is, gq(p, q) < 0. Then, if A and B are competitive products, the demand for A will increase; that is, fq(p, q) > 0. Reasoning similarly for complementary products, we arrive at the following test:
Test for Competitive and Complementary Products
Partial Derivatives | Products A and B |
fq(p, q) > and gp(p, q) > 0 | Competitive (substitute) |
fq(p, q) < and gp(p, q) < 0 | Complementary |
fq(p, q) ≥ and gp(p, q) ≤ 0 | Neither |
fq(p, q) ≤ and gp(p, q) ≥ 0 | Neither |
Use this test in Problems 91-94 to determine whether the indicated products are competitive, complementary, or neither.
92. Product demand. The daily demand equations for the sale of brand A coffee and brand B coffee in a supermarket are
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Chapter 7 Solutions
MyLab Math with Pearson eText - Stand Alone Access Card - for Calculus for Business, Economics, Life Sciences & Social Sciences, Brief Version (14th Edition)
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