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Khan Academy
Khan Academy: Addition Rule for Probability (Basic)
Venn diagrams and the addition rule of probability.
University of St. Andrews (UK)
University of St. Andrews: History of Set Theory
This page, which is provided for by the University of St. Andrews, traces the history of Set Theory as well as the concept of infinity and the infinite set.
PBS
Pbs Learning Media: Classifying Polygons
This interactive diagram focuses on sorting polygons by common properties and then you select the correct label for each section of the Venn Diagram.