Amazon calculates a product's star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers and factors that establish reviewer trustworthiness.
No complaint regarding the packaging. The book came in good condition. A must-have for SSC Exams. Though I think the content of the book could be organised in a better way if the words were categorized according to their homogeneity.