This volume is the eleventh in a series of 29 coordinated MINNEMAST units in mathematics and science for kindergarten and the primary grades. Intended for use by first-grade teachers, this unit guide provides a summary and overview of the unit, a list of materials needed, and descriptions of five groups of lessons. The purposes and procedures for each activity are discussed. Examples of questions and discussion topics are given, and in several cases ditto masters, stories for reading aloud, and other instructional materials are included in the book. In this unit, the operations of addition and subtraction of whole numbers are introduced and developed. Section 1 introduces the "a+b" notation and related addition to the joining of sets. In section two, subtraction is developed using missing addend problems. Later sections concern (3) grouping, even and odd numbers, and arrays; (4) introduction to the number line; and (5) numerals through 99. Three supplementary games are also included. (SD)