Algebra I Review Problem

justjess

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Aug 30, 2013
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Hello! I am a junior currently starting Algebra II. Unfortunately, I'm stuck on this one Algebra I review problem that we were assigned (looks like I already forgot all my Algebra I, uh oh). Here is the problem:

Solve for c : (xy)/4 = (a-2c)/(d-5c)

What I did was try and cross multiply, so I got: 4a -8c = xy(d - 5c) and then 4a -8c = -5cxy + dxy. However, I have no idea where to go from there, which makes me think I probably made a mistake in the steps leading up to that one.

Any help is appreciated, let me know if I need to clarify or explain anything! Should be a quickie. Thank you.

-Jess
 
Hello! I am a junior currently starting Algebra II. Unfortunately, I'm stuck on this one Algebra I review problem that we were assigned (looks like I already forgot all my Algebra I, uh oh). Here is the problem:

Solve for c : (xy)/4 = (a-2c)/(d-5c)

What I did was try and cross multiply, so I got: 4a -8c = xy(d - 5c) and then 4a -8c = -5cxy + dxy. However, I have no idea where to go from there, which makes me think I probably made a mistake in the steps leading up to that one.

Any help is appreciated, let me know if I need to clarify or explain anything! Should be a quickie. Thank you.

-Jess

You started out fine. Next collect all terms that have "c" in them on the left side of the equation, and put everything else on the right side:

5cxy - 8c = dxy - 4a

Now factor the c out of those two terms:

c(5xy - 8) = dxy - 4a

Finally, divide both sides by (5xy - 8) to get c by itself.
 
Now factor the c out of those two terms:

c(5xy - 8) = dxy - 4a
Note to the original poster: That "now factor the c out" is the "trick" that your instructor was figuring you'd forgotten. Make sure you understand what wjm did, and make sure you remember this for later. This will show up on a test! ;)
 
Thank you both, I had forgotten about that! Since this isn't for a grade, I bet we'll go over this in my next class. Thanks to this I'll have a head start. :)
 
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