There is a call for enabling students to use a range of efficient mental and written strategies when solving addition and subtraction problems. To do so, students should recognise numerical structures and be able to change a problem to an equivalent problem. The purpose of this article is to suggest an activity to facilitate such understanding in an algebraically fruitful way. Methods that make use of the associative rule for students to use a range of efficient mental and written strategies for addition and subtraction problems are examined, with an eye for making the transition to using the associative rule in algebra in later years.