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Homework Help: Finding errors

  1. Apr 2, 2010 #1
    1. The problem statement, all variables and given/known data
    [tex]\[
    \[
    \begin{array}{l}
    {\rm{A quantity Y is given by:}} \\
    Y = \frac{{4a^3 b}}{{\left( {5c^2 \sqrt {\rm{d}} } \right)}} \\
    {\rm{Find the error in Y given the following errors in a, b, c, and d:}} \\
    a \pm 1\% ,{\rm{ }}b \pm 0.5\% ,{\rm{ }}c \pm 2\% ,\,{\rm{ }}d \pm 1.5\% \\
    \end{array}
    \]
    \[/tex]



    2. Relevant equations
    Given above


    3. The attempt at a solution
    I plugged the numbers into this equation and got 0.1632993162
    This is not correct.
    I added all the percentage errors together to get 5%. Then asked myself why I did that anyway.
    Don't know how to solve this problem. I know how to find percentage errors but these are already given.
    please help. Thank you

    And also - My LaTex is not working properly - It doesn't recognize the spaces between the words from MathType. Anyone know why?
     
    Last edited: Apr 2, 2010
  2. jcsd
  3. Apr 2, 2010 #2
    When you combine errors in a formula containing powers with the terms multiplied and divided you add the percentage errors of all the terms, but with the additional factor that if a term is squared the % error is doubled, if it's cubed the % error is 3 times. etc etc.
    You can probably find a proof of this online.
     
  4. Apr 17, 2010 #3
    Thank you
     
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