在中学5—7年级学生的数学课堂上时常会遇到这样一类的现象和事实. a)解题时学生需要计算14与38的乘积,他在一张纸上或在课堂的黑板上,整齐地将一个数字写在另一个数字的下面,开始演算:4·8-32,写下2,记住3……等等. 但这些数字的相乘可以在心中计算,使14和40相乘,并从已得乘积中减去14的 In the mathematics classes of middle school students in grades 5-7, these phenomena and facts are often encountered. a) When solving problems, students need to calculate the product of 14 and 38. He is on a piece of paper or on a blackboard in class. Write a number neatly below another number and start the calculation: 4. 8 - 32, write 2, remember 3, etc. But the multiplication of these numbers can be calculated in mind, making 14 and 40 phases. Multiply and subtract 14 from the multiplied product