Two: conventional method. For example: 14+6+25+15+9+1+31+5+4 You can find that14+6 is 20 25+ 15 is 2 * 25.
3 1+5+4 is 2*20, so there are six 20s. If you want to add 6*20= 120, the answer comes out.
Question 2: how to use complement method to add and subtract quickly;
For example, 245+55 1 can be supplemented as: 240+550+5+ 1=790+6=796 (randomly written).
The complement should be an integer ten or an integer hundred less than this number.
Question 3: How to use the complement method for fast oral addition and subtraction;
For example, 245+55 1 can be supplemented as: 240+550+5+ 1=790+6=796 (randomly written).
The complement should be an integer ten or an integer hundred less than this number.
Question 4: Poor verbal calculation. How can I add and subtract quickly by oral calculation? Buy a dictation card and do it every day, and the calculation time will be shorter and shorter.
Question 5: How to quickly add or subtract12+6 = 29-7 = 33+2 = 3+40 =15+4 =100?
23+5= 37+ 1= 29-3= 38-3= 15-4=
18-2= 30+8= 43+ 1= 86+2= 70+3=
30-2= 72-2= 66-4= 39-2= 20-9=
53+5= 35+2= 39-4= 8+50= 20- 1=
40+6= 62+7= 89-5= 63+3= 34-2=
50-4= 1 1+2= 53-3= 60+8= 80-7=
32+4= 26-5= 84+4= 35- 10= 7 1+9=
18-4= 66+ 10= 83-3= 7 1+5= 60-5=
36+3= 58+30= 28-7= 87- 10= 80-6=
1 1+9= 80-3= 95-4= 64+3= 98-4=
25+7= 62-2= 83+5= 83+ 10= 10+8=
56+20= 64+6= 65+3= 15-3= 30-3=
32+6= 29-7= 35+2= 7 3+4= 25+4=
43+5= 87+ 10= 3 9-3= 48-30= 95-40=
8 1-2= 60+8= 39+ 10= 76+ 10= 70+30=
48-9= 47-8= 52-4= 43-8= 68-9=
40-2= 27-9= 32-4= 4 1-2= 38-9=
50-8= 63-9= 37-8= 56-20= 88-9=
75-9= 92-3= 42-7= 7 1-6= 58- 10=
47-8= 26-7= 52-3= 69- 10= 63-5=
80-2= 36-9= 78-4= 65-8= 99-9=
72-2= 45-9= 86-8= 96-2= 24-9=
40-2= 46-9= 43-4= 18-2= 38-8=
35+5= 85+2= 59-4= 78+ 10= 82-5=
64+6= 32+7= 49-5= 63+3= 84-2=
60-4= 1 1+20= 45-3= 30+8= 60-7=
25+4= 36-5= 84+4= 52-3= 7 1+9=
88-4= 76+0= 93-3= 18+5= 70-5=
56+20= 64+6= 65+3= 15-3= 30-3=
32+6= 29-7= 35+2= 7 3+4= 25+4=
43+5= 87+ 10= 3 9-3= 48-30= 95-40=
8 1-2= 60+8= 39+ 10= 76+ 10= 70+30=
48-9= 47-8= 52-4= 43-8= 68-9=
40-2= 27-9= 32-4= 4 1-2= 38-9=
30-2= 72-2= 66-4= 39-2= 20-9=
53+5= 35+2= 39-4= 8+50= 20- 1=
40+6= 62+7= 89-5= 63+3= 34-2=
50-4= 1 1+2= 53-3= 60+8= 80-7=
32+4= 26-5= 84+4= 35- 10= 7 1+9=
12+6= 29-7= 33+2= 3+40= 15+4=
23+5= 37+ 1= 29-3= 38-3= 15-4=
18-2= 30+8= 43+ 1= 86+2= 70+3=
30-2= 72-2= 66-4= 39-2= 20-9=
53+5= 35+2= 39-4= 8+50= 20- 1=
16+9= 5+ 18= 17+3= 36+6= 29+5= 87+9=
48+8= 35+8= 4+ 19= 7+26= 4+37= 29+4=
19......& gt& gt
Question 6: fast oral calculation addition and subtraction 1: subsidy method. For example: 136 minus 47, 50 plus 47' 136 minus 50 is easier to calculate, and 86 plus 3 is the answer. You can also subtract 40 first and then 7.
Two: conventional method. For example: 14+6+25+15+9+1+31+5+4 You can find that14+6 is 20 25+ 15 is 2 * 25.
3 1+5+4 is 2*20, so there are six 20s. If you want to add 6*20= 120, the answer comes out.
Question 7: How to do more problems quickly by oral calculation and addition? Practice makes perfect.
Question 8: How to talk about the skills of oral arithmetic teaching in primary schools quickly and accurately?
Nanhai Bian Computing, a senior math teacher in middle school, occupies a very important position in primary school teaching. It is an important part of primary school teaching content and the basis of learning mathematics. The requirements of the new curriculum standard: pay attention to oral calculation, advocate diversification of algorithms, and avoid complex calculation and stylized narration of "arithmetic".
However, in the long-term teaching process, only in the first grade, within 20 years of addition and subtraction teaching, teaching AIDS are used to train students in oral arithmetic. In the future, most of the teaching, except multiplication formula, is basically written calculation teaching, that is, vertical calculation teaching, and little thinking training is carried out in oral calculation teaching. The new curriculum standard requires students to gain understanding of mathematics while making progress and development in thinking ability, emotional attitude and values. Oral arithmetic can not only cultivate students' logical thinking ability, but also cultivate students' memory and attention, and improve students' interest in learning mathematics. Therefore, we must attach importance to the oral arithmetic training in primary school. Below, the author summarizes some methods and skills of oral calculation as follows. Please criticize and correct the addition and subtraction oral calculation within 20.
1, addition
There are many ways to train additive thinking within 20 minutes: counting, connecting, adding ten, oral calculation, deduction, subtraction and so on. According to different cultural environment, family background and their own thinking, it should be realized through students' own hands-on practice, independent exploration and cooperation and exchange. The emphasis here is on subtraction.
We stipulate that the two numbers that can make up 10 are complementary, 1 and 9, 2 and 8, 3 and 7, and so on. They complement each other.
The method is: subtract the complement of the second addend from the first addend and add 10. For example:
9+4= 13
Thinking method: the complement of the second addend is 6; The first addend 9 subtracts the complement 6 of 4 to get 3; Add 10 to 3 and you get 13. That is 9+4 = 9-6+10 = 3+10 =13.
This way of thinking is conducive to cultivating students' reverse thinking ability, but it can only satisfy students with strong thinking ability. Teachers can guide according to the situation.
Step 2 subtract
The subtraction of abdication within 20 is based on addition within 20, and the methods are: addition subtraction, division by ten, decomposition subtraction, decimal to large number, subtraction, addition, complement and so on. Here, we mainly introduce the supplementary methods:
The method is: add the complement of the minuend with the number in the unit, and remove the tenth "1", such as the minuend.
13 - 4 = 9
Thinking method: 3 in the minuend unit is not reduced enough; The complement of subtrahend 4 is 6; 6 plus 3 in the minuend gets 9, and the tenth "1" is removed.
Second, two-digit addition and subtraction oral calculation:
Two-digit addition and subtraction This paper focuses on the methods of subtraction and addition. First of all, we stipulate that two numbers whose sum is 100 are complementary to each other.
1, addition
There are four phenomena in the addition of two digits, that is, one digit and ten digits do not carry; Carry one digit, not ten digits; There is a decimal place and a single place without decimal place; All figures are rounded. The following are introduced respectively:
(1), two digits plus one digit plus ten digits do not carry, and they are added directly by the method of number synthesis.
For example: 34+52 = 30+50+4+2 = 86
(2) Two-digit addition, carry one digit, not carry ten digits. The way to think is:
One plus ten digits and another plus ten digits plus "1" get ten digits, and each digit subtracts the complement of 100 of the other digit and adds the digits to get the digits.
For example: 36+ 47 = 83
Oral calculation process: the number on the tenth digit is 3+4+ 1=8.
The number in the unit is 6-3(3 is the ten complement of 7) =3.
Or 7-4(4 is the ten complement of 6) =3.
So: 36+47 The decimal digit is 8, and the single digit is 3, which is equal to 83.
(3) Two digits plus decimal number, and one digit without decimal number. The way to think is:
Firstly, the number of digits in the "hundred digits" is determined as "1", then the digits are obtained by subtracting the complement of ten from the number of digits plus one, and the digits are added directly by the method of digit synthesis.
For example: 83+64 = 147
Oral calculation process: the hundred digits are "1".
The decimal number is 8-4 = 4 or 6-2 = 4.
The unit is 3 +4 = 7.
So: 83+64 hundred digits are 1, 10 digits are 4, and 7 digits are equal to 147.
(4) two-digit addition, all digits carry, thinking method is:
First, make sure one hundred ... >>