Word problem: ave. score S(t) = 68 - 20 log(t + 1)

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jshaziza

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Students in an English class took a final exam. They took equivalent forms of the exam at monthly intervals thereafter. The average score S(t), S(t)=68-20 log(t+1).

(a.) What was the average score when they initially took the test?

(b.) Graph the function.

For (a.), my question would be, is the 20 part of the log and if so would I change the formula to 68-log(t+1)^20 or do I do that only for the graphing? Thx. for your help. :)
 
I suppose you could do that with the log, but why?

S(0) = 60 -- There's the first answer. Graphing it is up to you. Just plot a couple of points. It may help to graph R(t) = log(1+t) just to get a feel for the smoothness and the general idea.
 
How did you get 60 as your first answer, I came up with 68, could you tell me how you did it?
 
When they initally took the test is represented by 0, so plugged in 0 for t, and than solved using the formula S(0)=68-20 log (0+1). So basically I did 68-20 log 1 on my calculator and got 68. I figured it was too easy, so what did I do wrong?
 
jshaziza said:
When they initally took the test is represented by 0, so plugged in 0 for t, and than solved using the formula S(0)=68-20 log (0+1). So basically I did 68-20 log 1 on my calculator and got 68. I figured it was too easy, so what did I do wrong?
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Isn't your problem:

S(t) = 60 - 20log(t+1)
 
Well, that would make a difference. 68 it is. Okay, now draw the graph.
 
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