Chapter 4 Quadratic Functions and Factoring - Mixed Review of Problem Solving - Lessons 4.6-4.10 - Page 316: 2a

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Let $x$ be the price of the drum and $n$ be the number of drums. Given: $n=50\\x=120$ When $n$ increases by $4$, $x$ decreases by $5$ Obtain: $n=50-\frac{4}{5}(x-120)\\=-0.8x+146$ The revenue: $n\times x=-0.8x^2+146$