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(a) Substitute t= 0 into the formula and calculate.
(b) Substitute t= 3 into the derivative function and calculate.
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Comment from student: For question b aren’t they asking for growth rate. And not the population at three hours.
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My response : Your comment/note is FAULT.
What I propose you to do, is EXACTLY about on how to calculate the growth rate, using the derivative.
If you do not understand it, it means that you are in wrong class.