Help with writing expressions / equations

M

mkroll

New member
Joined
Sep 18, 2011
Messages
4
Trying to help daughter with homework and it has been too many years since actually doing this type work.

Solve.

You are buying gifts for 10 people. You decide to buy each person either a CD or DVD.
A CD costs $12 and a DVD costs $20.

a. Let c = the number of CD's 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 CD's? For the cost of DVD's?

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


my work is as follows

for a. I came up with an expression of c = 10 - x

for b. I am guessing cost of CD's = c 12 "c times twelve" and cost of DVD's = x 20 "x times 20"

for c. I am clueless....

anyone that can help would be appreciated.

Thanks.
 
a) No good. What is "x"? Define that first. Is the number fo DVDs?

b) "12c" looks okay, but "20x" is still lacking a definition.

Let's assume x = # of DVDs. Then 20x = cost of DVDs.

x + c = 10, so x = 10 - c

c) 12c + 20x = 12c + 20(????)

What goes in there? It is a substitution of a previously-identified expression.
 
tkhunny said:
a) No good. What is "x"? Define that first. Is the number fo DVDs?

b) "12c" looks okay, but "20x" is still lacking a definition.

Let's assume x = # of DVDs. Then 20x = cost of DVDs.

x + c = 10, so x = 10 - c

c) 12c + 20x = 12c + 20(????)

What goes in there? It is a substitution of a previously-identified expression.
Click to expand...
------------------------------------------------------------------------------------


Yes, I made an assumption of:

c = # of CD's
x = # of DVD's

Hopefully this makes the solution for a. and b. better.

I get confused when the problem states "Write and simplify an expression in terms of c for the total cost of all the gifts you buy."

and Thank you much for the reply
 
OK - we have a good definition. Now, what goes in the "????", given that we know c + x = 10 and it used to say "x"?
 
OK here it goes, it feels like I was back in school here.

if we have a 12c + 20x = 12c + 20 (???)
we can substitute the x=10-c and create

12c + 20x = 12c + 20(10-c) and that could become 12c + 20x = 12c + 200 - 20c

which would then simplify by canceling the 12c and dividing by 20

back to x=10-c

this just doesn't seem right?
 
Whoa, there!! Why are you trying to solve an equation when we don't have an equation to solve?

Read the problem statement and don't overdo it.

You totally have the right expression at 12c + 200 - 20c.

Simplify that and you are done!
 
so... 200-8c

I so want to solve problems .... doesn't seem right to not have an = something.... thank you
 
Possibly you could use a better defintion of "solve".

Maybe...

"Solve" = Perform the required exploration as specified by the problem statement.

Note: Much of the study of mathematics is training your brain, not just manipulating little symbols. Don't get too hung up in the doing when there is so much thinking to do.
 
Help with writing expressions/equations

I have been beating my head over this last task that my daughter has had to do for her portfolio. Glad to know I'm not the only one who was having trouble helping my daughter. We were able to come up with a. 10-c=x (x being the number of DVDs) and b. 12c (cost of the CDs) and 12x (cost of the DVDs). For c. if c=5 and x=5, then 12(5) + 20(5) = 160.
 
Why do we care about c = 5? It's not in the problem statement. Are you making up some other problem?
 
You must log in or register to reply here.
Top