Question

You are buying gifts for 10 people. You decide to buy each person either a CD or a DVD. A CD costs $12 and a DVD costs $20.
a. Let c=the number of CDs you decide to buy. What is an expression in terms of c for the number of DVDs you buy?
b. What is an expression in terms of c for the cost of the CDs? For the cost of the DVDs?
c. Write and simplify an expression in terms of c for the total cost of all the gifts you buy. What properties of real numbers did you use to simplify the expression.

Answer 1

You just have to write it out like a sentence:

"The total cost is the number of DVDs I buy times $20 plus the number of CDs I buy times $12. The total number of gifts I buy is 10. This is equal to the number of DVDs I buy plus the number of CDs I buy"

Now transform the sentence into an equation using the following replacements:
c = "number of CDs I buy"
d = "number of DVDs I buy"
t = "The total cost"

"The total cost is the number of DVDs I buy times $20 plus the number of CDs I buy times $12. The total number of gifts I buy is 10. This is equal to the number of DVDs I buy plus the number of CDs I buy" becomes:

"t is the d times $20 plus c times $12. The total number of gifts I buy is 10. This is equal to the d plus c"

Now let's replace words like equals, plus, times...

t = d*$20 + c*$12
10= d + c

Answer 2

Now we can solve part a.) What is an expression in terms of c for the number of DVDs you buy?

Answer 3

We just need the second equation to do this, so starting with:
10 = d + c ...

Answer 4

so would it be 10d=c?

Answer 5

What is it ??? I'm on it right now