Addition and subtraction skills of pupils under 20 years old

Learn the tricks of addition and subtraction within 10 and 20.

Learn addition and subtraction within 10.

1, addition: remember a large number in your mind, count the decimal up, for example, 4+2= remember 4 in your mind, count up two numbers, 5 and 6, and then get the result 4+2=6.

2. subtraction: remember large numbers in your mind and count down decimals, for example, 6-3= remember 6 in your mind, count down 3, 5, 4, 3, and then get the result 6-3=3.

Parents need to cooperate with their baby to add and subtract within 30 kinds of 10 every day to improve their baby's arithmetic ability, and be careful not to let them count their fingers, so as to cultivate their baby's habits and mental arithmetic ability.

Tips for addition and subtraction in 20 minutes

No carry addition and subtraction within 20

1, 1 1-20 numbers can be used to play guessing games with children. Describe numbers in three ways:

1) bit is 2, and the tenth bit is 1.

2) 1 ten, five one.

3) greater than 1 1 and less than 13.

Describe the numbers in these ways and let the children guess, or vice versa, until they are proficient.

2. Dial the number with the counter. Parents say the number and children dial the number. A composition that is said while dialing. For example, 12 consists of 1 tens and 2 ones.

In the mathematics teaching of senior one, carry addition and abdication subtraction within 20 are both the focus and the difficulty of teaching. General children learn the addition and subtraction within 10 in preschool. After entering primary school, they can master the addition and subtraction within 20 with a little practice, without carrying or abdicating. However, it is not so easy for children to learn carry addition and abdication subtraction. The calculation speed and accuracy of some students have decreased greatly, and polarization has begun to appear. Some students began to drag their homework because they couldn't keep up with the calculation speed, which became a difficulty for math learners.

So, what makes it difficult for children to learn carry addition and abdication subtraction within 20? I think it has something to do with the algorithm we use to calculate carry addition and abdication subtraction. Algorithms are nothing more than counting and digital reasoning. Counting method is to calculate by counting, including counting by object and counting simply. Digital inference refers to the method of calculating with numbers, including ten-sum method and split method.

However, the digital reasoning method requires a lot of thinking steps, which is not conducive to students' mastery and eventually blurts out. Take the most widely used method of supplementing ten as an example. What's nine plus six? Students need these thinking processes before solving problems:

First, determine whether the problem is carry addition;

Second, if it is carry addition, how can I add it to 10? After the method is determined, the following operations can be performed:

9+6=9+( 1+5)=(9+ 1)+5= 10+5= 15

As can be seen from the above operation, this is a simple calculation process by using the law of addition and combination, which belongs to a class that cannot directly use the data in the question and needs to be split for simple calculation. Therefore, the seemingly simple method of supplementing ten is not simple in thought, it contains a series of logical reasoning processes. There is a certain distance between its cognitive basis and the knowledge structure and thinking ability of first-year students, which causes students' calculation difficulties to some extent. So, is there any way to solve this problem better? Here's what I did:

Carry addition within 20.

How do students master carry addition within 20 in a short time? In fact, as long as it is converted into the subtraction within 10 that students have mastered, the formula can be summarized as: "add nine and subtract one, add eight and subtract two, add seven and subtract three, add six and subtract four, and add five and subtract five." How to use the formula? Take "plus nine MINUS one" as an example. "Add nine and subtract one" refers to the addition of a number and 9, and the number minus 1 is the unit of their sum.

For example: 8+9= () take 8 and subtract 1 to get 7, and use 7 as the unit of summation, that is, 8+9= 17, 5+9= () take 5 and subtract 1 to get 4, and use 4 as the unit of summation, that is, 5+9 =/kloc-.

The method of "eight minus two, seven minus three, six minus four and five minus five" is the same as above.

Subtract abdication in 20 minutes.

The abdication subtraction within 20 is opposite to the carry addition within 20, that is, the abdication subtraction within 20 is converted into the addition within 10. The formula is: "minus nine plus one, minus eight plus two, minus seven plus three, minus six plus four, minus five plus five." How to use the formula? Take "minus nine plus one" as an example. "Minus nine plus one" means a number minus nine, and the result of adding 1 to this number is their difference.

For example, 17-9 = () take the 7th place of 17, and add 1, and the result is 8, that is, 17-9 = 8, 13-9 = () take/kloc-.

For example: 17-2 = () Distinguish between single digits and ten digits, and see whether the single digits can be simplified first. If 7-2 is enough, subtract it with 10, remember 7 in your mind, then count down 6 and 5 to get 5, and then 1 in ten digits remains unchanged, and get 15.

The method of "minus eight plus two, minus seven plus three, minus six plus four, minus five plus five" is the same as "minus nine plus one".

The first-year students can't think abstractly correctly. Using the above method, students who are used to relying on physical calculation can calculate the results quickly and accurately, avoid rote memorization and blind practice, improve the operation speed, reduce the error rate and reduce the learning burden of students.