The book " Probability and Statistics " by G. Balaji is a widely used resource for engineering students, particularly those under the Anna University regulations. While "exclusive" PDF copies are often hosted on private educational portals or document-sharing sites, the content typically follows the standard five-unit structure for engineering mathematics.
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MA3391 Lecture Notes: Comprehensive notes for Anna University's 2021 Regulation are available on EnggTree and BrainKart.