Help needed rearranging an equation and spotting errors.

[JimmyBrown]

Hi all,

Really struggling with this, hoping someone can help me.

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A student was asked to rearrange the formula:

. . . . .\(\displaystyle 9a\, =\, \dfrac{b}{3}\, -\, 2c(b\, -\, 7)\)

...to make b the subject (assuming that 6c - 1 is not equal to zero).

Below is the student's incorrect attempt:

. . . . .\(\displaystyle 9a\, =\, \dfrac{b}{3}\, -\, 2c(b\, -\, 7)\)

. . . . .\(\displaystyle 27a\, =\, b\, -\, 2c(b\, -\, 7)\)

. . . . .\(\displaystyle 27a\, =\, b\, -\, 2cb\, -\, 14c\)

. . . . .\(\displaystyle 2bc\, -\, b\, =\, -27a\, -\, 14c\)

. . . . .\(\displaystyle b(2c\, -\, 1)\, =\, -27a\, -\, 14c\)

. . . . .\(\displaystyle b\, =\, \dfrac{-27a\, -\, 14c}{2c\, -\, 1}\)

(i) Write out the correct rearrangement of the formula.

(ii) Identify two of the three mistakes made by the student. Explain, as if directly to the student, why their working is incorrect.

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Thought it would be easier to upload a screenshot of the question rather than write it out but if anyone needs anymore information then let me know. Thanks in advance.

 

[stapel]

Thought it would be easier to upload a screenshot of the question rather than write it out

:???:

A student was asked to rearrange the formula:

. . . . .\(\displaystyle 9a\, =\, \dfrac{b}{3}\, -\, 2c(b\, -\, 7)\)

...to make b the subject (assuming that 6c - 1 is not equal to zero).

Below is the student's incorrect attempt:

. . . . .\(\displaystyle 9a\, =\, \dfrac{b}{3}\, -\, 2c(b\, -\, 7)\)

. . . . .\(\displaystyle 27a\, =\, b\, -\, 2c(b\, -\, 7)\)

. . . . .\(\displaystyle 27a\, =\, b\, -\, 2cb\, -\, 14c\)

. . . . .\(\displaystyle 2bc\, -\, b\, =\, -27a\, -\, 14c\)

. . . . .\(\displaystyle b(2c\, -\, 1)\, =\, -27a\, -\, 14c\)

. . . . .\(\displaystyle b\, =\, \dfrac{-27a\, -\, 14c}{2c\, -\, 1}\)

(i) Write out the correct rearrangement of the formula.

(ii) Identify two of the three mistakes made by the student. Explain, as if directly to the student, why their working is incorrect.

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Really struggling with this... if anyone needs anymore information then let me know.

Since you've shown no work of your own, we have no idea with what, exactly, you're "struggling". So please reply with a clear listing of your efforts so far, starting with your own worked solution.

Please be complete. Thank you!

 

[JimmyBrown]

I'm struggling with the whole question, I haven't really got anything to show you in terms of how far I have got. I have a complete mind block with this one.
I have a scrap piece of paper covered with gibberish at the moment!

If someone is able to answer the question and explain it to me I would happily help back with someone in return. Just really don't know where to start with this one.

Thanks in advance.

 

[stapel]

I'm struggling with the whole question, I haven't really got anything to show you....I have a complete mind block with this one....Just really don't know where to start with this one.

Then the first step is to learn the underlying material. (I'm sorry you missed the weeks when they covered this in class!)

First, you'll want to learn how to solve regular linear equations in one variable. For that, start here. Study at least two lessons from the listing.

Then you'll need to learn how to solve literal equations (being equations in two or more variables, where you're needing to solve for one of the variables in terms of the others). For that, start here. Again, study at least two lessons from the listing.

Once you've learned the necessary terms and techniques, you can then attempt the exercise. If you get stuck, you will then be able to reply with a clear listing of your efforts so far, at which point we can begin to work with you. Thank you!