Posted by **Anonymous** on Monday, September 16, 2013 at 12:29pm.

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.

Write and simplify an expression in terms of c for the total cost of all the gifts you buy.

My answer- My expression is 12c + 20(10-c). When I use the distributive property, I get 12c + 200 - 20c. Now, when I simplify this even further, I get 32c + 200, which is not making sense.

- Math -
**Steve**, Monday, September 16, 2013 at 2:19pm
you should subtract that 20c, making

200-8c

note if c=0 all gifts are dvd's, costing 200.

Then since cd's are $8 cheaper, you save $8 for each cd bought.

- Math -
**Anonymous**, Monday, September 16, 2013 at 2:33pm
Thank you. Also, the problem asks about what properties of real numbers I used to solve this problem. So far, I am only seeing the distributive property. Is this the only one used?

- Math -
**Steve**, Monday, September 16, 2013 at 3:12pm
I suppose associative is also involved, since we have to use it to rearrange the

12c+200-20c

to be

200+12c-20c

then distributive again to get

200+(12-20)c

do you have some property that equates adding a negative and subtracting a positive?

- Math -
**Anonymous**, Monday, September 16, 2013 at 3:16pm
No.

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