Don't understand

  • #1

Main Question or Discussion Point

dont understand

For the following function, C computes the cost in millions of dollars of implementing a city recycling project when x percent of the citizens participate.
Using this model, approximately what is the cost if 60% of the citizens participate?
Using this model, estimate the percentage of participation that can be excepted if $5 million is spent on this recycling project? Set up an equation and solve algebraically. Round to the nearest whole percent
 
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Answers and Replies

  • #2
symbolipoint
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Do you have a function definition for C? Do you have sufficient information to find the function C?

Your information seems to become:
C=f(x); what is f(0.60)? what is x when 5=f(x)?... in other words, if C=5, what is f(x)?

More information is needed.
 
  • #3
C(x)=1.5x/100-x

his is the formula the book gives me
 
  • #4
Zurtex
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So x is the percentage and C is the total cost.

Replace x with 60 in the formula and see what C is.
 
  • #5
i did that a got like .04 but to me that doesn't seem right
 
  • #6
Zurtex
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i did that a got like .04 but to me that doesn't seem right
I assume the formular to mean this:

C(x)=(1.5x)/(100-x)

Right? In which case put 60 in and work out again.
 
  • #7
this is what i did
C(X)=1.5X/100-X
C(60)=1.5*60/100-60
C(60)=90/40
C(60)=2.25
C(60/60)=2.25/60
C=.0375 OR .04
so i'm suppose to put this in millions if i move the decimal point over six spaces then i get37,500 or 40,000
 
  • #8
Zurtex
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C(60)=2.25
C(60/60)=2.25/60
I don't understand why you suddenly decided to divide it by 60 here, I also don't understand why you think: C(x/60) = C(x)/60
 
  • #9
isnt the x in front of the C a 60 so to get C by itself you divide
 
  • #10
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isnt the x in front of the C a 60 so to get C by itself you divide
No it isn't. The notation C(x) means that C is a function of x, it is not multiplication of C by x. Often in math we use a shorthand and refer to a function f(x) by merely f, that is what is happening when they ask you for the value of C whe x=60, or C(60), that is the function C(x) evaluated at the number 60, not C "times" 60.
 
  • #11
ok i think i get it now, so my answer would be 2.25, put that into millions and i get 2,250,000
 

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