Z = (mean1 - mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√n
If only one SD is provided, you can use just that to determine SEdiff.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability
Hope this helps.
A flour mill produces flour in small bags before distributing them to wholesalers. The average weight of each bag is 8 kg with a standard deviation of 0.5 kg. A random sample of 50 bags was taken and found that the average weight is 7.8 kg. Using a significance level of 0.01, test the hypothesis that µ = 8 kg against the alternative where µ ≠ 8 kg. (Then, construct the 99% confidence interval)
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