The document discusses workbooks as a supplement to mathematics textbooks. It defines a workbook as a modification of a textbook that provides exercises and activities for students to reinforce concepts without having to copy from the textbook. The document outlines key functions of workbooks, including saving time by eliminating copying, facilitating grading of work, and providing individualized practice. It also describes characteristics of effective workbooks, such as being authored by experienced teachers, providing a variety of graded exercises, and including answer keys. In conclusion, the document notes that workbooks are commonly used in elementary and middle schools because they allow students to work directly in the book and are more portable than textbooks.