How To Calculate Confidence Intervals? Please Help!?

The sample is 16 houses. The average sale time is 250 days. The population standard deviation is 55 days. I’m supposed to use the tables with the z-scores.
The question is:
Construct a 90% confidence interval of the mean sale time for all homes in the neighborhood.
How do I do this? Thank you.

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One Response to “How To Calculate Confidence Intervals? Please Help!?”

  1. BeeFree says:

    SmiileToday
    CI = mean +/- (z*)(standard deviation) / sqrt n
    where z* = 1.645 from Normal table with 10% / 2 = 0.05 area in each tail
    CI = mean +/- (z*)(standard deviation) / sqrt n
    CI = 250 +/- (1.645)(55) / sqrt 16
    CI = (227.4, 272.6)
    hope that helped

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