arithmetic builtin function

例句：

1. 1. The teacher explainedthe problem using arithmetic.
   老师用算术解释了这个问题。
2. 2. Arithmetic is anessential skill for students in mathclass.
   算术是数学课学生必备的技能。
3. 3. The student was able to solvethe problem using arithmetic.
   学生能够使用算术解决这个问题。