It is necessary to consider measurements of amounts based on the definition of expressing measurements with two units, such as when “3 l and 2 dl” is written as “3 l 2 dl,” as well as the definition of writing measurements with different units, as in the case where “10000 ” is written as “1 ha.”
Also, in order to achieve a concrete grasp of the set of numbers, it is necessary to express numbers in a variety of concrete models, and to take advantage of knowledge about the definition of these representations.
There is a model referred to as the “number line” which is used for expressing numbers (see Figure 20). This involves placing an origin point (0) on a straight line, determining the unit size (1), and using this to correspond numbers to points on the line. Use this model based on the definition of this representation.