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Homework Help: Standard Deviation Question

  1. Apr 22, 2010 #1
    1. A voltmeter is used to measure a known voltage of 100V. Forty percent of the readings are within 0.5V of true value. How do I figure out the standard deviation of the voltmeter, and how do I figure out the probability of an error of 0.75V?

    2. I am trying to figure this problem out, however I do not know what to do with the 40% of the readings. Is that my n? Is n=40? And is the mean (99.5+99.6+99.7+99.8+99.9+100+100.1+100.2+100.3+100.4+100.5)/40? I am doing circles trying to figure this out.

    Thanks for any input and help, OEstudent
  2. jcsd
  3. Apr 23, 2010 #2


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    Homework Helper

    You have a 40% CI of 100V ± 0.5 V

    Most likely your readings are normally distributed. So you need to get the Zα value and use the formula for the CI.
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