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Rearranging a formula

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    For the formula:

    Click image for larger version. 

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    I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

    I got:
    a=8-4c
    44-----
    444b-c

    But I got the wrong answer:confused:
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    (Original post by krisshP)
    For the formula:

    Click image for larger version. 

Name:	Screenshot.png 
Views:	26 
Size:	1,017 Bytes 
ID:	139205


    I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

    I got:
    a=8-4c
    44-----
    444b-c

    But I got the wrong answer:confused:
    Its not allowed to post full solutions.

    Can you show your working, then i can tell you where you went wrong.
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    (Original post by krisshP)
    For the formula:

    Click image for larger version. 

Name:	Screenshot.png 
Views:	26 
Size:	1,017 Bytes 
ID:	139205


    I have to make a the subject. What is the right answer? Please explain HOW you get the correct answer with working out. Thanks.

    I got:
    a=8-4c
    44-----
    444b-c

    But I got the wrong answer:confused:
    You forgot to multiply ab by 4 when getting rid of the fraction.
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    when multiplying ab by 4 I get a wrong answer of

    8-4c
    -------=a
    4b-c

    Here I first multiplied by 4 and expanded to get:
    4ab-ca+4c=8
    Then I -4c to get:
    4ab-ca=8-4c
    After this I factorised the LHS to get:
    a(4b-c)=8-4c
    Then I divided both sides by (4b-c) to get the answer stated above.

    WHY did I fail?
  5. Offline

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    (Original post by krisshP)
    when multiplying ab by 4 I get a wrong answer of

    8-4c
    -------=a
    4b-c

    Here I first multiplied by 4 and expanded to get:
    4ab-ca+4c=8
    Then I -4c to get:
    4ab-ca=8-4c
    After this I factorised the LHS to get:
    a(4b-c)=8-4c
    Then I divided both sides by (4b-c) to get the answer stated above.

    WHY did I fail?
    What is the final answer supposed to be?
  6. Offline

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    (Original post by krisshP)
    when multiplying ab by 4 I get a wrong answer of

    8-4c
    -------=a
    4b-c

    Here I first multiplied by 4 and expanded to get:
    4ab-ca+4c=8
    Then I -4c to get:
    4ab-ca=8-4c
    After this I factorised the LHS to get:
    a(4b-c)=8-4c
    Then I divided both sides by (4b-c) to get the answer stated above.

    WHY did I fail?
     \displaystyle ab - \frac{c(a+4)}{4} = 2

    Multiply throughout by 4,
     \displaystyle 4ab - c(a+4) = 8

\displaystyle 4ab - ac -4c =8
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    Not sure but I know that the answer of:

    8-4c
    ------ = a
    4b-c

    is wrong.

    What answer do you get? Is it the same as if it is it could mean that mymaths is wrong.
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    (Original post by krisshP)
    Not sure but I know that the answer of:

    8-4c
    ------ = a
    4b-c

    is wrong.

    What answer do you get? Is it the same as if it is it could mean that mymaths is wrong.
    I have indicated your mistake in my previous post.
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    Thanks Raheem94 for making me learn from a mistake
  10. Offline

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    (Original post by krisshP)
    Thanks Raheem94 for making me learn from a mistake
    You are welcome.

    By the way, what answer do you get, so that i can confirm if you are right or wrong.
  11. Offline

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    I entered the new answer on mymaths and I got a tick, so the new answer was correct
    Thanks

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