it is important to deepen the understanding of the interrelationship between addition and subtraction for example "children were playing of these children, six went home, leaving eight children how many were there at the start ?" (from "Exciting Arithmetic 2, First Half" ). By having children consider situations such as this. it is becomes possible to clarify for them the relationship between the whole amount and a partial amount. while they think about the relationship between addition and subtraction. It is important to give consideration to how this ties in with ways of thinking both sequentially and in reverse sequential order (Figure 5)