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.
I bought this book to help me move through excel with practical applications. I found that Excel 2010 is very different from the version which the author was using. This being said, it actually caused more confusion than clarity. I recommend buying a version which is more up-to-date.