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Homework Help: Simple Uncertainty/Sig Fig Question

  1. Mar 29, 2016 #1
    1. The problem statement, all variables and given/known data
    This is for a lab. I have two values that I need to subtract, so I am pretty sure I am supposed to add up uncertainty. I have also been told that the uncertainty decimal places should match up with the decimal places on the value itself.

    50.00mL ± 0.05mL – 14.3mL ± 0.1mL =

    2. Relevant equations

    3. The attempt at a solution
    35.7mL ± 0.15mL???
  2. jcsd
  3. Mar 29, 2016 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Matching up the decimal places between error and value is generally right, why do you know one pair of values to two decimal places and the other pair to only one? It seems odd.
    Assuming there is a good reason for that, there are two more points to consider. Generally,one argues that you would be unlucky for the errors to reinforce to the maximum extent, so instead take a statistical approach. Specifically, take the root sum square of the errors. Next, you cannot quote more decimal places in the answer than your worst case input value.
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