The first example in Table 1 shows that students used inappropriate concepts to manipulate-b-b. Therefore, two items were constructed based on this alternative conception. Similarly, in the second two examples, students were unable to simplify 3a-6a or -6a+3a correctly. Thus, four items involved positive and negative integers were constructed to investigate students' computational skills in manipulating these integers. Also, four expanded items were constructed based on -b-b and 3a-ba. The expanded items were: