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What did I do wrong?

  1. Sep 17, 2009 #1
    A random sample of 530 households resulted in the following frequency distribution for a number of cars per household. Find the mean and standard deviation.
    Number of cars ¦ Frequency
    1 ¦ 61
    2 ¦ 108
    3 ¦ 179
    4 ¦ 118
    5 ¦ 64
    Sorry don't know how to put this in a box. Under cars it's 1,2,3,4,5. Under frequency it'a 61,108,179,118,64. I typed the Freq. into my calculator and my mean was 106 and my standard deviation was 48.13.
    I was marked off 6 points. Shoud I have just done cars? Put that into my calculator and my mean would be 3 and my sd be 1.6?
  2. jcsd
  3. Sep 17, 2009 #2
    Try re-reading the problem then try to understand the question. It's asking you to find the mean number of cars, right? Your answer was 106. Does that make sense? Do you really think the mean number of cars per household is 106? I wish I had that many cars...
  4. Sep 17, 2009 #3
    The mean would be 3 and the sd be 1.6 ? Thanks
  5. Sep 17, 2009 #4
    If you're rounding, 3 is the mean. On the other hand, 1.6 seems a bit off.
  6. Sep 17, 2009 #5
    Sd comes out to 1.58.
  7. Sep 17, 2009 #6
    You should post the steps you are taking to solve the problem. That way we can see where you are making an error and correct it.
  8. Sep 17, 2009 #7
    Oh god, I just realized how you're coming up with mean = 3 and stdev = 1.6.....

    Re-read the question, and again try to understand the question. After you've done that, answer this: what is the total number of cars?
  9. Sep 21, 2009 #8
    Hint: Look up weighted means (of an ordered categorical variable). That's all I'm going to say. If you come back, someone else may help you.
  10. Sep 21, 2009 #9
    Thanks I got it now.
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