Chapter 1 - Equations and Inequalities - 1.5 Applications and Modeling with Quadratic Equations - 1.5 Exercises - Page 135: 63

$4\ weeks$

Step 1. Assume the manager should wait $x$ weeks, the yield per tree would be $100+5x=5(x+20)$ Step 2. The price per pound would be $40-2x=2(20-x)$ Step 3. The revenue per tree would be $R=5(x+20)(2)(20-x)=10(400-x^2)$ Step 4. Let $R=3840\ cent$, we have $10(400-x^2)=3840$ or $x^2=16$ thus $x=4\ weeks$