Students in calculus course were given a exam and each month thereafter they took an equivalent exam.The class average on the exam taken after t months is F(t)=86-6 ln(t+1).
How many times has an equivalent exam been given if the average score is decreasing at a rate of one point per month.

You are being asked to find the solution of:



CB

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Truth does not change because it is, or is not, believed by a majority of the people.

Giordano Bruno

F(t)=86-6ln(t+1)
= 86- 6 ln 2
= 86-4.15
= 81.8 ...??

is this what we are supposed to do?

or like shall i be plugging in f(-1) ?

You solve for -1, because the function gives the rate of change for the grades, in this case -1, when you solve for in this instance it will tell you how many months has passed and according to the problem one test a month

Differentiate F(t) with respect to t (which gives the rate of decrease in scores per month), then set that equal to -1 and solve for t (because that is what is asked for).

CB

__________________
Truth does not change because it is, or is not, believed by a majority of the people.

Giordano Bruno

Alright ..

So here is what I have done
f(t)=86-6ln(t+1)
f'(t)= 6 (1/t+1)
now f'(t)=-1

6/(t+1)=-1
6=-t-1
6+1=-t
-7=t

Is this correct?

Does a negative value of t seem reasonable to you? If not, then perhaps you should check your work to see if you've made a careless mistake somewhere.

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There are two things you should never try to prove: the impossible and the obvious.

The greater danger for most of us lies not in setting our aim too high and falling short; but in setting our aim too low and achieving our mark. (Michelangelo Buonarroti)

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