Addition and subtraction within 20 minutes. I learned addition and subtraction in 20 minutes, and it was a mid-term exam. An exam that tests students' knowledge for half a semester helps students formally test their usual learning level. According to this result, students can adjust their learning mentality and methods in time and carry out the next stage of learning more efficiently. The mid-term exam mainly examines students' academic performance in the first half of the semester. Students should be prepared before the exam.