Key to Decimals Answers and Notes: Books 1-4 The Key to Decimals series begins with basic concepts and operations on decimals. Then it covers real-world uses of decimals in pricing, sports, metrics, calculators, and science. The success-oriented approach of Key to Decimals builds confidence and independence. You'll find this series to be a great way to prepare for standardized tests. This is the Answers and Notes book but it does include the complete text of all 4 of the student Key to Decimals books along with some teaching tips.