en.wikipedia.org/wiki/Statistics
byjus.com/statistics-formulas/
https://stattrek.com/statistics/formulas.aspx
ec.europa.eu/eurostat/statistics-explained/index.php/Beginners:Statistics_4_beginners
betterexplained.com/articles/a-brief-introduction-to-probability-statistics/
www.opentextbooks.org.hk/system/files/export/9/9418/pdf/Principles_of_Business_Statistics_9418.pdf
elitedatascience.com/learn-statistics-for-data-science
