Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.
However, depending on the degree and direction of the skew, the probability may not apply.
A student group claims that first year students at a university study 2.5 hours (150 minutes) per night during the school week. A skeptic suspects that they study less than that on average. He takes a random sample of 30 first year students and finds that X=137 minutes and sx=45 minutes. A graph of the data shows no outliers but some skewness. Carry out an appropriate significance test at the 5% significance level. What conclusions do you draw?
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