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Give an example of a real-world cost that depends on an unknown amount of something. Try to create an expression to represent the total cost.

Answer :

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Answer:

Ok, let's suppose that the unknown amount is the number of books you buy in a library. (let's represent this unknown quantity with the variable X)

We know that each book costs $9.75, and we know that in total cost for the X books is $68.25

Then, how many books do you get?

We know that if one book costs  $9.75, then X books will cost X times $9.75

Then the total cost is:

C(X) = X* $9.75

And we know that the total cost was $68.25

Then to solve this, we need to solve the equation:

X* $9.75 = $68.25

X = $68.25/$9.75 = 7

The equation that can be used to represent the information is the cost of a book is $3, find the number of books when a customer pays $21.

To represent the scenario, the cost of a book is $3, find the number of books when a customer pays $21.

Therefore, the number of books will be:

3x = 21

x = 21/3

x = 7

In conclusion, the correct option is $7.

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