Rice textbook: read the first 3 sections about probability
https://onlinestatbook.com/2/probability/probability.html

Watch the videos and answer the questions (**linked above)

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Readings:

Stats Stuff: Read the Normal Distribution section up through Empirical rule.
https://www.usu.edu/math/schneit/StatsStuff/Probability/probModels9.html

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More on the Normal Distribution