What is a rational number? This is an extension of the concepts learned in book 15 and includes decimals. More work with positives and negatives.
There are 20 books in the Pre-Algebra series. The first books continue from the Fraction series with more work on fractions and decimals. Books progress through percentages, proportions, metrics, scientific notation, order of operations and finally, probability in Book 20. Students who complete the Pre-Algebra series are now fully ready for Algebra (coming soon).