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Khan Academy

Khan Academy: Smith, Marx, and Keynes

For Students 9th - 10th
Spanning three centuries of history, from the dawn of the industrial age to modern times, three diverse thinkers developed their own landmark theories on commerce, labor, and the global economy. The three economists profiled in this...
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University of Toronto (Canada)

U. Of Toronto: Basic Principles of Marxian Economics [Pdf]

For Students 9th - 10th
With all references made to Capital, this very advanced work can be read with Marx's texts, providing helpful insight and definition to the terms, ideas, and even format. Not for beginners, however.