Students use of the equals sign in the context of arithmetic and algebra. The concept of the equals sign in arithmetic is to"do something"(Bodin& Capponi, 1996). In algebra, an equal sign signifies an equation. Many students tried to add"=0" to algebraic expressions when they were asked to simplify(Kieran,1997) This kind of error indicates an absence of knowledge of the difference in meaning of an expression and an equation. This can be one of the factors contributing to the alternative conceptions, or perhaps a misunderstanding of the objective in simplifying an expression. Tirosh, Even and Robinson (1998) investigated four teachers awareness of students' tendency to conjoin or finish open expressions. They pointed out that the procedural thinking students frequently face difficulties accepting lack of closure. They think of an open expressions such as 4x+2 ,as incomplete and tend to solve them, like finding the final numerical answers in arithmetic.