Matrix about coins

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thunc14

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Same situation as my last question, I am lost as to how to approach the problem. Typically when I see this kind of problem, it's usually a system of equations or some kind of equation modeling. I'm not sure exactly what to do with the matrices and how to represent the problem using a 3x3.
 

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thunc14 said:
Same situation as my last question, I am lost as to how to approach the problem. Typically when I see this kind of problem, it's usually a system of equations or some kind of equation modeling. I'm not sure exactly what to do with the matrices and how to represent the problem using a 3x3.
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Did you set-up the equations that you would need to solve to answer the "word problem"?

If you did - please show us.
 
Let d= the number of dimes you have
Let n = the number of nickels you have
Let q = the number of quarters you have.
Now follow the previous post.
 
The problem bothers me, because the fact is that you do not need any matrix at all! And if you choose to use a matrix, and there are several possible ways to do it, then none of them are specifically needed. One is clearly valid; others may also be, but that is the wrong question for them to be asking.
 
The 3 equations I would have set up given the information are:
q + d + n = 50
q = .25(d+n)
.25q + .1d + .05n = $5.65

I'm not sure why this is a matrix problem and not just a system of equations problem, and I'm not familiar with setting up a 3x3 matrix in this capacity.
 
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thunc14 said:
The 3 equations I would have set up given the information are:
q + d + n = 50
q = .25(d+n)
.25q + .1d + .05n = $5.65

I'm not sure why this is a matrix problem and not just a system of equations problem, and I'm not familiar with setting up a 3x3 matrix in this capacity.
Click to expand...

Please tell us what you have learned about matrices and systems of equations, if anything. If you know nothing about it, then you can't be expected to answer the question. (As I've said, you don't need to use matrices at all, so the wording of the problem is silly. But you can use matrices, and one is most clearly usable.)

There are two main ways to use matrices for this purpose. The one most directly related to this problem is explained here. Another, using augmented matrices (with an extra column), is here.
 
I'm very familiar and comfortable with solving systems of equations. I remember next to nothing about matrices. After reading that article, choice A looks like it could properly represent the situation, but it uses .5 instead of .05, so that screws up the nickel bit for the equation representing the total amount of money.

After following the steps of your link (thank you very much Dr. Peterson), I don't see a matrix that would be used to arrive at a solution, which isn't an answer choice so I'm clearly doing something wrong. I've attached the work I've done so far.
 

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thunc14 said:
I'm very familiar and comfortable with solving systems of equations. I remember next to nothing about matrices. After reading that article, choice A looks like it could properly represent the situation, but it uses .5 instead of .05, so that screws up the nickel bit for the equation representing the total amount of money.

After following the steps of your link (thank you very much Dr. Peterson), I don't see a matrix that would be used to arrive at a solution, which isn't an answer choice so I'm clearly doing something wrong. I've attached the work I've done so far.
Click to expand...
I did not verify your inverse, but the end result has the correct values

For the record, .79999.... equals EXACTLY .8
 
Hey Jomo,

I used the calculator in the link Dr. Peterson put up to get the inverse. It's weird how it gets the correct values when you use 0.05. Am I correct in saying that none of them are correct? I wonder if that 0.5 is a typo for 0.05. I don't see how the other 2 are relevant as they aren't the inverse matrix.
 
Dr.Peterson said:
The problem bothers me, because the fact is that you do not need any matrix at all! And if you choose to use a matrix, and there are several possible ways to do it, then none of them are specifically needed. One is clearly valid; others may also be, but that is the wrong question for them to be asking.
Click to expand...
It seems like they are all wrong. Choice A assigns the nickels a value of .5, not .05, which makes that matrix incorrect. The others just appear to be nonsensical to me, but None of the Above is not an answer choice so I'm not sure what I'm missing here. Terrible matrix question imho
 
I had missed the erroneous 0.5 when I judged that that was one of the matrices they call "needed". I hadn't tried finding the inverse of either that or the correct one. I agree; it's not a problem worth wasting time on.
 
Problem is I need to come up with an answer for this problem. Besides the typo, the others just seem erroneous to me. I have no idea what the answer is to this bizarre question is.
 
Why can't you say (d), More than one is incorrect? That is true when all are incorrect!

But, yes, it's a very bad problem in multiple ways, and I wouldn't be surprised if its creators have the wrong answer themselves.
 
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