Z = (score-mean)/SEm
SEm = SD/√n
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to each Z score.
Suppose the weights of Farmer Carl's potatoes are normally distributed with a mean of 8.0 ounces and a standard deviation of 1.2 ounces.
(a) If 4 potatoes are randomly selected, find the probability that the mean weight is less than 9.8 ounces.
(b) If 8 potatoes are randomly selected, find the probability that the mean weight is more than 9.1 ounces.
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