Science:Math Exam Resources/Courses/MATH102/December 2015/Question 08
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Question 08 

Ecologists observe that the product of a species’ population density, , and its average metabolic rate, , is a constant across species. Thus, . If a species evolves over time with its population density increasing at a constant rate, what do you expect to be happening to the species’ metabolic rate? (a) Metabolic rate increases at a constant rate. (b) Metabolic rate increases at a nonconstant rate. (c) Metabolic rate decreases at a constant rate. (d) Metabolic rate decreases at a nonconstant rate. 
Make sure you understand the problem fully: What is the question asking you to do? Are there specific conditions or constraints that you should take note of? How will you know if your answer is correct from your work only? Can you rephrase the question in your own words in a way that makes sense to you? 
If you are stuck, check the hint below. Consider it for a while. Does it give you a new idea on how to approach the problem? If so, try it! 
Hint 

Write it into a function form and then check the derivative 
Checking a solution serves two purposes: helping you if, after having used the hint, you still are stuck on the problem; or if you have solved the problem and would like to check your work.

Solution 

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Please rate my easiness! It's quick and helps everyone guide their studies. If D increase and DM is a constant, then M should at least decrease. Now leaves us (c) and (d). Suppose D=t, which satisfies the description "D increases at a constant rate",( you can also be more precise like D=D0 + at, but it is not necessary since we just wanna check if rate is constant). Then "DM=C" becomes "tM=C", then "M=C/t", thus the derivative of M is not a constant. answer: 