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and her expenses are
Thus her profit is
If she increases the price to $(20 + 1) her sales reduce to (30  1) per week and her expenses are $10 × (30  1) per week so her weekly profit is
If she increases the price to $(20 + 2) her sales reduce to (30  2) per week and her expenses are $10 × (30  2) per week so her weekly profit is
Now I can see the pattern. If she increases the price to $(20 + x) her sales reduce to (30  x) per week and her expenses are $10 × (30  x) per week so her weekly profit is
This is the profit function so you can use the calculus you know to maximize this function. Write back if you need more assistance,
Hi Joe. If you don't know calculus, you can still solve the problem. When you set the expression Penny wrote equal to "y" and multiply it out, you get a quadratic function. This means a parabola. You'll find, if you check, that this parabola opens downward. That means that the If you write the quadratic function in vertex form, you can answer the question by just reading off the y value of the vertex. See Cheers,  


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