Official Guide Explanation:
Problem Solving #171

Background

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Solution and Metadata

Question: 171
Page: 84
Difficulty: 6 (Moderately Difficult)
Category 1: Algebra > Equations >
Category 2: Word Problems > Profit >

Explanation: Profit is always given by revenue minus costs. Costs in this case are easy: the number of pounds purchased (x) times the cost per pound (p): xp. Revenue is a bit harder: number of pounds sold, which is the number of pounds purchased minus those discarded due to spoilage (x - y), times sale price per pound (s): s(x - y). Profit, then, is:

Revenue - Cost

(x - y)s - xp, choice (A).

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