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Thread: Calculating relative and absolute error

  1. #1
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    Calculating relative and absolute error

    A =5 , B =4.8 and C = 0.2. The relative error on A, B and C is 1%. Calculate the absolute and relative error on D when D is calculated as

    D =A/C + B/C

    Explain why the relative error in D is large.


    I'm new to this topic and got a little confused, we don't get any solutions so here is my attempt.

    ABSOLUTE D = l0.5/0.02l + l-0.048/0.02l = 27.4

    RELATIVE D = 0.02/0.5 + 0.03083/0.5 = 0.0816

    I calculated the relative error of A, B and C using the formula lerror/valuel

    I know these will most likely be wrong but could someone give me guidance on how I might correct these?

    Thanks
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  2. #2
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    Re: Calculating relative and absolute error

    It looks like you put the absolute and relative errors for A, B, and C into the formula for D. Why in the world did you do that?

    If the measured value for A was 5 with 1% relative error, the absolute error was plus or minus 0.05 so A could be as large as 5.05 or as low as 4.95. Similarly, the measured value for B was 4.8 with 1% error so B could be as large as 4.8+ 0.048= 4.848 or as low as 4.8- 0.048= 4.752. Finally, the measured value for C was 0.2 with 1% error so C could be as large as 0.2+ .0002= 0.2002 or as low as 00.2- 0.002= 0.198. The value for D could be as large as (5.05+ 4.848)/0.198= 50 or as low as (4.9+ 4.752)/2.002= 48.2. (5+ 4.8)/0.2= 49 so the absolute error in D is 1.00 and the percentage error is 1/49 or about 2%.
    Thanks from NixLUKE
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  3. #3
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    Re: Calculating relative and absolute error

    AH! that helped me understand what I'm supposed to be doing a lot better! thank you!
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