8. The cost in dollars, [tex]\( C \)[/tex], of installing a sewer pipe that is [tex]\( L \)[/tex] feet long is modeled by the function below:

[tex]\[ C(L) = 300 + 20L \][/tex]

Given that function, what is the most logical interpretation of the following equation?

[tex]\[ C(20) = 700 \][/tex]

A. The cost to install a 700-foot sewer pipe is 20 dollars.
B. 20 times the cost of a typical pipe is equivalent to 700 dollars.
C. The cost to install a 20-foot-long sewer pipe is 700 dollars.



Answer :

To determine the most logical interpretation of the equation [tex]\(C(20) = 700\)[/tex] given the cost function [tex]\(C(L) = 300 + 20L\)[/tex], let's go through the steps to understand what this function represents and how the given values fit into it.

1. Understand the given cost function:
[tex]\[ C(L) = 300 + 20L \][/tex]
This equation states that the cost [tex]\(C\)[/tex] for installing a sewer pipe consists of a fixed cost of [tex]$300 plus an additional $[/tex]20 for each foot of the pipe. Here,
- [tex]\(300\)[/tex] is the fixed cost.
- [tex]\(20L\)[/tex] is the variable cost that depends on the length [tex]\(L\)[/tex] of the pipe in feet.

2. Interpret the given value:
- The equation [tex]\(C(20) = 700\)[/tex] involves substituting [tex]\(L = 20\)[/tex] feet into the cost function.

3. Substitute [tex]\(L = 20\)[/tex] into the cost function:
[tex]\[ C(20) = 300 + 20 \times 20 \][/tex]

4. Calculate the cost:
[tex]\[ C(20) = 300 + 400 = 700 \][/tex]
This calculation confirms that for [tex]\(L = 20\)[/tex] feet, the cost is $700.

5. Interpret the calculated result:
The calculated cost [tex]\(700\)[/tex] corresponds to installing a pipe that is [tex]\(20\)[/tex] feet long.

Given the options, let's examine which matches our interpretation:
- (A) The cost to install a 700-foot sewer pipe is 20 dollars.
- This is incorrect because it misinterprets both the cost and the length in the context of the cost function.
- (B) 20 times the cost of a typical pipe is equivalent to 700 dollars.
- This is incorrect because it does not directly relate to the cost function given or to the interpretation of the calculated result.
- (C) The cost to install a 20-foot-long sewer pipe is 700 dollars.
- This is correct because it directly matches the interpretation of our calculated result.

Therefore, the most logical interpretation of the equation [tex]\(C(20) = 700\)[/tex] is:
[tex]\[ \boxed{\text{(C) The cost to install a 20-foot-long sewer pipe is 700 dollars.}} \][/tex]

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