This publication is part of a series of guides written by Pennsylvania's Department of Public Instruction and is designed to present some of the unifying concepts in mathematics to elementary teachers. This pamphlet discusses the commutative, associative, and closure properties for addition and multiplication of whole numbers, and the distributive property. Numeration systems, including decimal and non-decimal systems, are briefly described. Short exercise sets are included for each section, along with an answer key. (Related documents are SE 015 951 and SE 015 952.) (DT)