precal
posted by laura on .
A cell phone company’s profit is modeled by the function p(x) = 10x − x2 − 1, where p is expressed in thousands of dollars and x is the number of phones sold in hundreds. How many phones must the company sell to make a profit of more than $15,000?

P(x) = 10x  x^2  1 = 15.
x^2 + 10x  1  15 = 0.
x^2 + 10x  16 = 0.
Solve using Quadratic Formula and get:
X = 2 = 200 Phones.
X = 8 = 800 Phnes. 
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