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i am having trouble with this

can some one help me with this!

 

from 1985 to 2000, The percent P of total of music
sales with a certain format is modeled by P=5.9t – 11,706, where t is the year.

(A) Evaluate
P for t =1985 and t=2000

(B)  Use
your results from part (a) to graph the equation from 1985 to 2000

(C)  In
what year was P = 76.3%?

 

(A) P=  ?   for
t=1985

Round
to the nearest tenth as needed

 

P=  ?   for
t = 2000

 

Round
to the nearest tenth as needed

 

 

(C ) in what year was P=76.3%?

      

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2 Answers

Hi Crystal!  If I understand correctly, your question is more about how to graph the equation, rather than solving it, since the values for t are already determined (e.g., the years 1985 through 2000).  For example, if t = 1988, then P = 1988 times 5.9 minus 11706, which comes to 23.2.
 
To find all the values for P, you can calculate them manually (like above), but I'd recommend using a spreadsheet.  Start in cell A1 and enter 1985 (for the first year).  Put the rest of the years down column A until you have the value 2000 in cell A16.  Next, put your formula in cell B1.  The formula should look like this:  =A1*5.9-11706 (where A1 refers to the cell address in the spreadsheet, and * is the multiplication symbol).  Copy the formula down column B, from cell B1 to cell B16.  You can now find the answers to parts a and c of your question.
 
To plot the graph, highlight the range B1 through B16, and select Insert > Line > Line chart to create a simple graph of your equation. Hope that helps!
 
Bill Whitmore
X
Crystal,
This problem is a variant on y = mx + c. You have P = 5.9t – 11,706, with y being P, m = 5.9, x = t and c = -11706.  
 To evaluate P for t = 1985 and 2000, substitute these values in the equation to get the values of P (in percent). The values are ~ 5 and 94.
  Looking at the equation, what type of a curve would you expect for the function P? 
For part c, place P = 76.3 in the equation and find the year t that corresponds to it. Hope this helped.