ABSTRACT
This chapter looks at the most common types of number and examines some aspects of the structures. It considers natural numbers, integers, rational numbers and real numbers. Negative integers have positions on the number line even though they lack cardinal values. The need to extend the number line in response to practical situations requires other sorts of numbers as well as integers. Together the rational and irrational numbers make the real number system. In primary school, children should be introduced to the fraction form of rational numbers by discussing various models so that they understand the notation. The decimal form of rational numbers appears much simpler, but children are inclined to carry over intuitions from their experience with natural numbers. In primary school, children are introduced not only to numbers but also to ways in which they may be combined or acted upon.
