Many years ago, some people advocated "learning while playing, playing with middle school", and they have been obsessed with it: if only learning was as happy as playing! How easy it would be if you could learn while playing! This is also my little wish and pursuit!
Play math.
The second unit of mathematics in the second volume of the first grade of People's Education Press is "abdication subtraction within 20".
The abdication subtraction within 20 and the carry addition within 20 are equally important for further learning mathematical knowledge such as multi-digit calculation, which is the most basic knowledge. Therefore, when students study this part of the content, they should learn the calculation method on the basis of understanding arithmetic, and they need to achieve a certain proficiency through reasonable practice, so as to lay a good foundation for future study.
Observation of calculation method
When students calculate the subtraction of abdication within 20 years, there will be many methods such as "breaking ten methods, continuous subtraction, addition and subtraction". Individual children still use the method of reducing the total number one by one when starting to calculate, and the calculation speed will be very slow. The method given in the textbook is "addition and subtraction by breaking ten methods", so why doesn't the textbook present continuous subtraction? Even the essence of subtraction and subtraction (the meaning of subtraction) are more closely related. Since we want to advocate the diversity of algorithms, why not propose this method?
When learning more than ten MINUS nine in class, we first calculate it by hands-on operation. At that time, several children were able to calculate the numbers by mouth when they wrote 12-9. What do they think when asked? However, there is no reasonable expression. Several children said that if 12 removes nine objects, there will be three objects left. Let them take out 65,438+02 sticks first (prompt others to see 65,438+02 sticks at a glance), put ten sticks (a pile) in a bundle, and then put two more. When nine sticks are to be removed, children will draw nine sticks directly from 10, and the remaining 1 sticks and two sticks add up to three. Isn't this description the logic of "breaking the ten laws"? (It seems that this method is more intuitive, more operational and more in line with children's thinking characteristics. )
Then it is 13-9, 14-9, 15-9 ... Children will find that when more than a dozen people subtract 9, as long as more than a dozen people subtract 9, they will first take 9 from 10 and leave 1. I'll tell you the method when I win the first prize in calculation: as long as it's greater than ten MINUS nine, I'll add 1 to the unit (minuend). Actively discover, verify and summarize in the observation operation.
Then when learning more than ten MINUS eight, seven and six, the children observe and summarize according to the method of more than ten MINUS nine, which is fast and accurate. At the same time, I will write a chart of the oral calculation process under the formula, so that children can try to write it in the same way and express it with mathematical symbols.
For several children who are prone to make calculation mistakes, let them talk about the calculation process with a small stick in pairs after class, and gradually become proficient in the process of talking about the algorithm to speed up the calculation.
Application of digital card
Before subtraction learning, write the carry addition 36 within 20 on the digital card, and randomly draw cards every day for quick oral calculation. This digital card is cut into rectangles with discarded cardboard, and the formula is written down for easy access.
Let the children make a digital train and play a digital splitting game. For example 12 = ()+() = ()+() = ()+ ().
These are all preparations for abdication and subtraction in 20 years, because "I want to do addition and subtraction" is the fastest and best way for children to understand.
Learn to abdicate and subtract in 20 minutes, write down 36 subtraction questions on a cardboard card and answer them quickly every day.
Game 1. Answer board
Practice oral arithmetic in groups of three: 1 person plays cards, one person quickly tells the result, and the other person is the referee or answers first. Roles take turns.
Scene two. Sit in rows
After learning to abdicate and subtract in 20 minutes, organize the cards in groups of three or five.
When playing for the first time, I put a card first, and then let them see which card is related to mine. For example, if I put 12-4, some children will put their own 13-4 at the bottom or back, some children will put 12-5 next to them, and some children will take out cards equal to 8 ... In such activities, children will find out the arrangement rules of these formulas and understand the abdication within 20 in the process of placing. Such activities can allow children and their peers to observe, associate, communicate and reason together, not only to study the calculation results, but also to develop their thinking ability in the game.
Scene three. The flowers are blooming.
The game of blooming flowers and falling flowers is also the arrangement of abdication subtraction formulas. The difference is that it is arranged according to the result of the formula.
Take the difference as stamens, and the corresponding formula is petals. When making, let them think of a few petals first, then think of a good shape. In order to make it easier for them to find the rules, we subtract a few petals from 10, which is also the basis of the law of breaking ten.
For example, if you write =2 in stamens, first think about who subtracts who equals 2. The child's first thought is 10-8=2. Who else? 1 1-9=2. Anything else? Children will say 3- 1, 12- 10, etc., reminding them to write the formula of abdication subtraction again (one digit is subtracted from one dozen, starting from 10).
Children's creativity is particularly good, and the petals created are beautiful. At the same time, it is also found that from 10, you subtract a few, and then you end up subtracting nine from ten. The length of a stamen has several petals (formula), and the number of these petals increases simultaneously from one direction. ...
Be prepared in advance
Many people will think that the method of breaking ten is a calculation method, and addition and subtraction are not abdication subtraction. Looking back, I will find that there are many exercises in Senior One about Figure 4, and the latter Figure 3 is to let students feel the relationship between addition and subtraction. Therefore, this kind of addition and subtraction is the most familiar method for children, and it is also the easiest way for them to understand and master. The math teacher who read this article should pay attention. We should guide children to pay more attention to the relationship between addition and subtraction in the first grade, so as to prepare for the later calculation teaching.
In practice, children will also choose different methods to calculate, for example, it is easier to choose the ten-break method for larger digital subtraction, and it is easier for continuous subtraction and digital subtraction that they want to add and subtract.
On calculation speed
The standard (20 1 1) puts forward the goal of doing 8- 10 questions per minute by the end of the semester. However, in the early stage of learning, children must not be required to complete 50 questions in 5 minutes to be qualified. On the one hand, a large number of one-off practice tests will make children feel afraid of difficulties, and at the same time, qualified calculations cannot be measured by this measurement method.
The initial exercise is 10-20 crossing. Of course, it will be different according to the actual situation of the class, but we must pay attention to designing rich and varied exercises to improve students' computing ability.