SOLUTION: A population of microorganisms grows according to the function p(x) = 100+0.2x+0.5x^2, where x is given in hours. How many hours does it take to reach population of 250 microorgani

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Question 1192769: A population of microorganisms grows according to the function p(x) = 100+0.2x+0.5x^2, where x is given in hours. How many hours does it take to reach population of 250 microorganisms?
Answer by ikleyn(52778) About Me  (Show Source):
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A population of microorganisms grows according to the function p(x) = 100+0.2x+0.5x^2,
where x is given in hours. How many hours does it take to reach population of 250 microorganisms?
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To answer the question, you should solve this quadratic equation

    100 + 0.2x + 0.5x^2 = 250.


Reduce the equation to the standard form quadratic equation

    0.5x^2 + 0.2x - 150 = 0


and apply the quadratic formula.  You will get the roots

    x%5B1%5D = -17.5217,   x%5B2%5D = 17.1217.


According to the meaning of the problem, you ignore the negative root and accept the positive one.


Your ANSWER is the value  x= 17.1217 hours.

Solved.

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On solving quadratic equations using the quadratic formula,  see the lessons
    - Introduction into Quadratic Equations
    - PROOF of quadratic formula by completing the square
in this site.