There are many kinds of oral calculation methods, and how to find the best oral calculation method is the key to improve the speed and accuracy of oral calculation. When practicing, you can review a variety of oral calculation methods with students, so that students can get the best method through comparison.

Method 1: Do subtraction and want to add. Do the inverse of addition with subtraction and think with addition. For example, 12-8, Xiang 8+( )= 12.

Method 2: break the ten methods. For example, 13-7 can be thought as follows: 10-7+3=6.

Method 3: continuous subtraction (commonly used method), such as 13-7. You can think of it this way: 13-3-4=6, which means dividing 7 by 3 and 4. Method 4: Supplementary method. For example, 13-7 can also think like this: 13- 10+3=6.

Second, audio-visual combination, strengthen oral calculation

Oral calculation is the basis of written calculation, which has the characteristics of less time, large capacity, vivid form and fast speed. Therefore, oral arithmetic training can promote the formation of first-year students' computing ability and cultivate the agility of thinking.

Visual arithmetic and listening are two basic forms of oral arithmetic training. It is considered to count by eyes, brain calculation and mouth; Listening and calculation can only be achieved by listening and recording. In oral arithmetic training, the forms of oral arithmetic are often changed, and the combination of visual arithmetic and listening arithmetic can be used alternately, which can improve students' interest in oral arithmetic.

The content of oral calculation should be targeted. Different classes have different oral calculation contents. Exercises before new classes should give full play to their inspiring functions. For example, before teaching "8 plus several", the oral math problem can be designed like this:

8+2+ 1 8+2+3 8+2+5

8+2+2 8+2+4 8+2+6

The function of this group of questions is to induce thinking, put "arithmetic" into practice, and lay a solid foundation for calculating "eight plus several" through "adding ten".

In addition, pay attention to the level of practice. For example, the consolidation exercise of "ten minus seven" in teaching can be designed as follows:

7+( )= 13 7+( )= 15

13—7= 15—7=

This kind of exercise enables students to master the thinking method of "adding while doing subtraction". We think that whether the exercise is effective or not, we should highlight the word "clever". It not only takes less time, but also has the characteristics of large capacity, vivid form and fast speed, so as to review old knowledge and improve computing power.

Build ten, break ten, or even ten.

For example, the lesson "How many bottles of milk are there" on page 72 of the textbook lists 9+5=? After the formula, the textbook presents students with possible methods: (1) adding one by one; (2)9+ 1= 10, 10+4= 14; (3)5+5= 10, 10+4= 14; (4) 10+5= 15,9+5= 14。 Among them, method (1) and method (2) are all ten methods (the difference between the complement of one addend and another addend is the single digit of the sum, and it is decimal into one), which is relatively simple. But when students add and sum, it will be easier for them to use the method of dividing large numbers into decimals to make up ten. Of course, it should be easy for people. The purpose of the textbook is to encourage students to explore calculation methods independently, exchange and discuss the characteristics of various algorithms, and promote students to reflect in communication, so as to adjust and choose their own algorithms independently. It is worth noting that students may master more than these methods, and each student is not required to master four methods. At the same time, there is no best method for all students, and teachers should fully respect students' thinking and choices. As the saying goes,' teaching has the law, and the law is inconclusive'. Among them, method (2) and method (3) are both ten-point methods of dividing and calculating, but the difference is that some students are used to dividing large numbers into decimals, while others are used to dividing large numbers into decimals. In addition, the textbook also provides an algorithm based on the previously discovered mathematical laws: 10+5= 15, and 9 is 1 smaller than 10, and introduces 9+5= 14, which not only makes students feel the application value of mathematical laws. On this basis, courses such as "How many trees are there", "Buy pencils" and "Skydiving Performance" also lead to corresponding formulas through practical problems, which can enable students to solve problems independently, explore and experience the diversity of algorithms independently and exchange their own algorithms.

Here we take "buying a pencil" as an example to specifically introduce various calculation forms of abdication subtraction. Textbooks: There are 15 pencils, and 9 pencils have been sold. How many pencils are left? In order to solve this problem, the textbook does not adopt a unified method, but puts forward four thinking strategies: (1) restore one by one; (2) Divide 15 into 10 and 5, 10-9 = 1,1+5 = 6; (3) Divide 9 by 5 and 4, 15-5 = 10,10-4 = 6; (4)9+6= 15, 15-9=6。 Method (2) commonly used by students, called "breaking ten methods". First divide the two digits by 10 and the unit, and subtract from 10, and then the sum of the two is the required number. It can also be summed up in one sentence: the gain number is the sum of the complement of reduction and the number of minuend. Method (3) is called "flat ten method". First, subtract the number of the same bit from the minuend to get 10, and then subtract the remainder of the minuend from 10. In order to facilitate students' memory, I simplify it to: the number of results is the complement of the difference between the minuend and the minuend, which is called "anti-subtraction" interestingly. The inspiration of method (4) is that students are good at addition and subtraction, which can make them want to add and subtract: () +9= 15, traveling 6. In fact, this is a good way to solve problems by judging known conditions by adding and subtracting relations, and it also exercises students' logical thinking ability. This addition-subtraction relationship is "Addendum+Addendum = sum,-Addendum = another Addendum; Minus-Minus = difference, Minus-Minus = Minus, Minus+Minus = Minus, Minus+Minus = Minus ". It can be seen that it is very helpful for students to learn addition and subtraction by reflecting the diversity of algorithms and providing students with time and space to choose their own algorithms and communicate with each other.