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Thread: Make k the subject of an equation - no answers please, just direction

  1. #1
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    Make k the subject of an equation - no answers please, just direction

    I have read my tutorial book over and over but i still cannot understand how to make k the subject of the below equation.

    I really need to understand how this works so please do not give me any answers - just direct me and explain where I go wrong.

    The question asks I make k the subject of;

    t= 9s/5+4k

    I begin by multiplying both sides by (5+4k) giving

    t*(5+4k) = 9s/5+4k*(5+4k)

    Simplifying gives me

    t(5+4k)=9s (i think)

    multiplying both sides gives me

    5t+4kt=9s

    I want to find all the terms that contain the required subject, k, and move them to the left.

    4kt=5t+9s

    Now i want to subtract and then divide by t which gives

    k=5t-9s/4t

    Im stabbing in the dark with parts of this equation. Any direction would be appreciated

  2. #2
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    Quote Originally Posted by Luffy View Post
    I have read my tutorial book over and over but i still cannot understand how to make k the subject of the below equation.

    I really need to understand how this works so please do not give me any answers - just direct me and explain where I go wrong.

    The question asks I make k the subject of;

    t= 9s/5+4k

    I begin by multiplying both sides by (5+4k) giving

    t*(5+4k) = 9s/5+4k*(5+4k)

    Simplifying gives me

    t(5+4k)=9s (i think)

    multiplying both sides gives me

    5t+4kt=9s

    I want to find all the terms that contain the required subject, k, and move them to the left.

    4kt=5t+9s

    Now i want to subtract and then divide by t which gives

    k=5t-9s/4t

    Im stabbing in the dark with parts of this equation. Any direction would be appreciated
    Before we start on making k the subject of the formula, I should remind you that formulas sometimes need parentheses and, according to your workings, this is one of those times. That is, you equation is
    t = 9s / (5+4k)
    not
    t= 9s/5 + 4k.

    That said, you need to put k on the left hand side by itself. You are correct up to
    5t + 4kt = 9s
    but, subtracting 5t from both sides gives
    4kt = 9s - 5t
    not what you have. Your statement of dividing by t [actually 4t] is also correct but, as before, you will need some punctuation (parentheses) to format the answer correctly.

    -Ishuda

  3. #3
    Elite Member
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    Quote Originally Posted by Luffy View Post

    t= 9s/5+4k
    As Ishuda points out, there is a huge difference between
    t = 9s / 5 + 4k and t = 9s / (5 + 4k);
    make sure you understand why...
    I'm just an imagination of your figment !

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