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.
This was a great follow up to the first installment of this series. My 8 yr old son received the first book as a gift from his Little League coach and seemed to fly through the first and did the same with the second. He's anxiously waiting for the 3rd book to be released.