Question 7 • Algebraic Reasoning
The quadratic C(x) = 400x − 0.2x² opens downward because the coefficient of x² is negative, so its vertex gives the maximum cost. The vertex occurs at x = −400 ÷ (2 × −0.2) = 1,000 units. Substituting gives C(1,000) = 400(1,000) − 0.2(1,000)² = $200,000, so the true statement is that 1,000 units have the maximum cost of $200,000.
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