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    This is the question

    --------------------------
    t = 1 2 3 4 5
    m = 24 28.9 34.5 41.5 49.8

    It is believed that a formula such as m = ab^t connects m and t.

    Find the values of a and b.

    -------------------------------------

    I've done
    ln m = ln a + tlnb

    then I've used the scatter graph and regression calculator as follows:

    entered x values with the t values
    entered y values with ln m values

    then I've looked at rg ax+b and got a =0.182 and b = 2.9


    The answer in the book is a=20, b= 1.2.


    I would appreciate some pointers.

    Thanks
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    (Original post by maggiehodgson)
    This is the question

    --------------------------
    t = 1 2 3 4 5
    m = 24 28.9 34.5 41.5 49.8

    It is believed that a formula such as m = ab^t connects m and t.

    Find the values of a and b.

    -------------------------------------

    I've done
    ln m = ln a + tlnb

    then I've used the scatter graph and regression calculator as follows:

    entered x values with the t values
    entered y values with ln m values

    then I've looked at rg ax+b and got a =0.182 and b = 2.9


    The answer in the book is a=20, b= 1.2.


    I would appreciate some pointers.

    Thanks

    I have just put the values into this regression calculator and I get what the book gets

    http://www.easycalculation.com/stati...regression.php

    Oh - I see what you have done

    you have a and b the wrong way round and you have forgotten to raise e to the power
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    (Original post by TenOfThem)
    I have just put the values into this regression calculator and I get what the book gets

    http://www.easycalculation.com/stati...regression.php

    Oh - I see what you have done

    you have a and b the wrong way round and you have forgotten to raise e to the power

    Thanks - what with a and b in the question and and b on the calculator I got in a real muddle and then didn't do the final step.
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    (Original post by maggiehodgson)
    Thanks - what with a and b in the question and and b on the calculator I got in a real muddle and then didn't do the final step.
    easily done
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    (Original post by maggiehodgson)
    Thanks - what with a and b in the question and and b on the calculator I got in a real muddle and then didn't do the final step.
    So change the letters in the question to something different from a and b, rather than using the same letters to stand for two different quantities (a useful hint for all Maths).
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    (Original post by tiny hobbit)
    So change the letters in the question to something different from a and b, rather than using the same letters to stand for two different quantities (a useful hint for all Maths).
    Thanks. Yes I did that in order to discover where I went wrong. I will remember that lesson.
 
 
 
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