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Math Help - Formula

  1. #1
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    Formula

    hello,

    i have the following formules:

    a = ?
    b = (a + 650 * 2a/5.5) + (a * 450)
    c = (b / 4) - 270

    when i enter a = 30, c will be 10238.

    now i need a formula where i can enter d = 10238, and it calculates f = 30.

    I'm really confused, i hope somebody can help me.

    Thanks
    ~ Frank
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  2. #2
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    More information please

    Hello Frank

    Welcome to Math Help Forum!
    Quote Originally Posted by frank9999 View Post
    hello,

    i have the following formules:

    a = ?
    b = (a + 650 * 2a/5.5) + (a * 450)
    c = (b / 4) - 270

    when i enter a = 30, c will be 10238.

    now i need a formula where i can enter d = 10238, and it calculates f = 30.

    I'm really confused, i hope somebody can help me.

    Thanks
    ~ Frank
    I think you will need to clarify this question if you want a helpful answer. You have mentioned a, b and c, and then you ask for a formula that gives the value f = 30, when d = 10238.

    This doesn't really make a lot of sense. Could you give us some more information please?

    Grandad
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  3. #3
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    Better explaination

    ok ill try to explain it again,

    i have the following formules:



    when i enter a = 30 in the formule above, it will return c = 10238.

    now i need a formula where i can input any type of C value, and it will return the corresponding a value according to the formula used above.

    For example i put in c = 10238, it will return a = 30.


    Thanks
    ~ Frank
    Last edited by frank9999; January 6th 2010 at 09:33 AM. Reason: changed formula
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  4. #4
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    Hello Frank
    Quote Originally Posted by frank9999 View Post
    ok ill try to explain it again,

    i have the following formules:



    when i enter a = 30 in the formule above, it will return c = 10238.

    now i need a formula where i can input any type of C value, and it will return the corresponding a value according to the formula used above.

    For example i put in c = 10238, it will return a = 30.


    Thanks
    ~ Frank
    I understand now what you require - you simply need the inverse formula. However, I do not understand how the formula you have quoted gives c = 10238 when a = 30.

    You have:
    b = (a + 650 \times 2\tfrac{a}{5.5}) + (a\times450)
    The part that is unusual is 2\tfrac{a}{5.5}. This really means 2+\tfrac{a}{5.5}. So when a = 30:
    b = (30 + 650 \times (2+\tfrac{30}{5.5}))+(30\times 450)
    = 18375.45...
    and this then gives:
    c = 4323.86...
    Please clarify what you mean by 2\tfrac{a}{5.5}. Once you have done this, we may be able to reverse the formula to get a in terms of c.

    Grandad
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  5. #5
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    Quote Originally Posted by Grandad View Post
    Hello FrankI understand now what you require - you simply need the inverse formula. However, I do not understand how the formula you have quoted gives c = 10238 when a = 30.

    You have:
    b = (a + 650 \times 2\tfrac{a}{5.5}) + (a\times450)
    The part that is unusual is 2\tfrac{a}{5.5}. This really means 2+\tfrac{a}{5.5}. So when a = 30:
    b = (30 + 650 \times (2+\tfrac{30}{5.5}))+(30\times 450)
    = 18375.45...
    and this then gives:
    c = 4323.86...
    Please clarify what you mean by 2\tfrac{a}{5.5}. Once you have done this, we may be able to reverse the formula to get a in terms of c.

    Grandad
    It didn't mean 2 + (a/5.5), i wanted to say 2^(a/5.5) (to the power of) or however you say that in english:P

    so 2^(a/5.5) = 2^(30/5.5) = 2^5.5 = 45

    b = (30 + 650 * 45) + (30 * 450) = 42780

    c = 10425, depends on how you round some numers.

    hope that helped a bit.
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  6. #6
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    Hello Frank
    Quote Originally Posted by frank9999 View Post
    It didn't mean 2 + (a/5.5), i wanted to say 2^(a/5.5) (to the power of) or however you say that in english:P

    so 2^(a/5.5) = 2^(30/5.5) = 2^5.5 = 45

    b = (30 + 650 * 45) + (30 * 450) = 42780

    c = 10425, depends on how you round some numers.

    hope that helped a bit.
    I see. In that case, it is impossible to find a formula which will enable you to work backwards. The only thing I can suggest is that you set up these equations in a spreadsheet (e.g. Excel) and then use a Goal Seek tool to give you the answer.

    Grandad
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