Applications of derivatives

jessi_helt

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I'm having trouble with the following problem: Epidemiologists have found a new communicable disease running rampant in a college. They estimate that t days after the disease is first observed in the community, the percent of the population infected by the disease is approximated by p(t)= (20 t^3-t^4)/1000. Also t is greater than or equal 0 and less than or equal to 20. After how many days is the percent of the population infected a maximum?
 
I'm having trouble with the following problem: Epidemiologists have found a new communicable disease running rampant in a college. They estimate that t days after the disease is first observed in the community, the percent of the population infected by the disease is approximated by p(t)= (20 t^3-t^4)/1000. Also t is greater than or equal 0 and less than or equal to 20. After how many days is the percent of the population infected a maximum?
You titled this "Applications of derivatives". What is the derivative of p(t)? What does the derivative have to do with finding maximum values?
 
You titled this "Applications of derivatives". What is the derivative of p(t)? What does the derivative have to do with finding maximum values?

That's what I'm having the problem with, finding p'(t), I'm not sure if its because it is just a whole number in the denominator. I'm guessing like other extrema, after finding the derivative you would set it equal to 0 and then solve for t, but I'm kind of lost on the whole problem for some reason.
 
solve p'(t) = 0, if p''(t) < 0 at this point, you find the local maximum.
compare the local maximum with p(0) and p(20), you will find absolute maximum value in [0,20].
 
That's what I'm having the problem with, finding p'(t), I'm not sure if its because it is just a whole number in the denominator.
That is a polynomial: \(\displaystyle \frac{20}{1000}t^3- \frac{1}{1000}t^4= \frac{1}{50}t^3 - \frac{1}{1000}t^4\). The derivative of \(\displaystyle t^n\) is \(\displaystyle nt^{n-1}\).
 
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