1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Standard deviation and average value

  1. Mar 7, 2010 #1
    1. The problem statement, all variables and given/known data
    Students measured an object 5 times, and got the results 11,25 cm, 11,20 cm, 11,22 cm, 11,18 cm i 11,25 cm. The height of this object is:

    A. h = (11,22 ± 0,03) cm
    B. h = (11,22 ± 0,04) cm
    C. h = (11,25 ± 0,07) cm
    D. h = (11,25 ± 0,03) cm

    2. Relevant equations
    Standard deviation and average value formulas.

    3. The attempt at a solution

    I calculated the average value (11.22) and the standard deviation (0.03), so the answer should be A. But in the book, B is the correct answer. Am I missing something here?
    Last edited: Mar 7, 2010
  2. jcsd
  3. Mar 7, 2010 #2


    User Avatar
    Science Advisor

    This question does NOT ask for standard deviation and has nothing to do with standard deviation. It is true that the average is 11,22. The largest data value, 11,25= 11,22+ ,03 but the smallest is 11,18= 11,22- 0,04. All those numbers lie in the range [itex]11,22\pm 0,04[/itex]
  4. Mar 7, 2010 #3
    Thanks, i didn't know about that.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook