The calculation power of decimal division

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2. When I teach the calculation of decimal multiplication and division, I find that some students have difficulty in mastering the calculation method of decimal division; Some students make a lot of mistakes in the calculation of decimal multiplication and division, and the calculation accuracy is not very high. For primary school students to strengthen the teaching of calculation, effectively improve the accuracy of calculation is a very important aspect of primary school mathematics teaching. So what causes students to make mistakes? I think about my present teaching.

3. First, the grasp of knowledge is not firm. It may be that the basic concepts and calculations are not clear, or that the oral and written calculations are not accurate, so the calculation will be full of errors. Mathematical knowledge is based on a series of mathematical concepts. The calculation method of decimal multiplication and division is based on the calculation of integers. It is composed of a series of mathematical concepts such as "digit", "indivial digit", "addition", "full ten", "first digit" and "entering one". If the concept is not clear, it can not be calculated correctly according to the rules, laws, properties, formulas and other mathematical knowledge. The addition and subtraction of numbers within 20 and multiplication and division of numbers within 100 are the basis of four decimal operations. Because any four decimal operations can be decomposed into some basic oral problems. If you are not familiar with oral arithmetic, there will be mistakes in calculation. As long as there is an error in one step of the calculation, it will lead to an error in the calculation result of the whole problem
Second, it should be the students' psychological reasons. Students often use the word "careless" to explain calculation errors, but in addition to the errors caused by bad learning habits, it is more psychological reasons
the form of calculation problem is monotonous, which is composed of a series of data and symbols. However, pupils tend to be more general when they perceive the characteristics of things. Therefore, it often happens that the number or decimal point is copied wrong. Students' perception also has strong selectivity, thus ignoring the comprehensive and overall understanding. Students will be interested in some of the number features first intake of mind, and cover up the rest. The stability of attention of primary school students is poor. If they are asked to allocate their attention to two or more objects at the same time, there will often be the phenomenon of neglecting one or the other. Moreover, when the data in the calculation problem is large, the number of decimal places is large, or the shape of the formula is too complex, it will proce rejection psychology, showing impatience, can not seriously examine the problem, and no longer patiently choose a reasonable algorithm, so the error rate will increase.

4.

Decimal multiplication and division method calculation rule:

1, decimal multiplication calculation rule:

first calculate the proct according to the integer multiplication calculation rule, and then see how many decimal places there are in the factor, count several decimal places from the right side of the proct, the decimal point on the point; If the number of digits is not enough, use & quot; 0" Complement

2. Division algorithm of decimals:

first move the decimal point of divisor to make it an integer, and then move the decimal point of divisor to the right by several digits; 0"， Then calculate according to the division rule that divisor is an integer< br />

5. six point eight four ÷ 0.912＝7.5
25.84 ÷ 1.7＝15.2
99.6 ÷ 41.5＝2.4
220.5 ÷ 147＝1.5
36.8 ÷ 16＝2.3
1.25 ÷ 0.25＝5
0.72 ÷ 3.6＝0.2
1.62 ÷ 6＝0.27
1.535 ÷ 0.75＝2.046
1000 ÷ 12.5＝80
12.5 ÷ 5＝2.5
37.5 ÷ 6＝6.25
67.5 ÷ 15＝4.5
28.8 ÷ 12＝2.4
1.2 ÷ 3 0.48 ÷ 6 4.6 ÷ 23 14 × 0.5
6.8 ÷ 4 0.72 ÷ 12 0.7 × 1.1 0.72 ÷ 4
9.6 ÷ 6 5.2 ÷ 13 12.5 ÷ 5 0.12 × 5
8 ÷ 0.5 0.32 ÷ 16 0.5 × 1.1 0.5＋0.14
1.25 × 4 6.3 ÷ 2.1 0.92 ÷ 4 6 ÷ 1.2
0.4 ÷ 8=0.05 7.6 ÷ 3.8=2 6.8 ÷ 1.7=4 0.56 ÷ 14=4
2.4 ÷ 0.6 =4 84 ÷ 0.04 =2100 0.49 ÷ 0.7 =0.7 6.3 ÷ 3.1=2
96 ÷ 0.6 =160 1.55 ÷ 0.5 =3.1 0.35 ÷ 0.07 =5 36 ÷ 1.2 =30
4.8 ÷ 3＝1.6 1.8 ÷ 0.5＝3.6 0.05 ÷ 4＝ 0.0125 0 ÷ 5.32＝0
13.2 ÷ 6＝ 2.2 33.5 ÷ 5＝ 6.7 3.6 ÷ 18＝ 0.2 0.54 ÷ 2.7＝0.2
OK There is also decimal multiplication< br />1.5 × 4= 6
2.5 × 4 = 10
0.13 × 4= 5.2
5.4 ÷ 10= 0.54
4.2 × 1000= 4200
0.45 ÷ 0.15= 3
3.6 ÷ 0.1= 36
8.5 × 100= 850
3.2 ÷ 100= 0.032
0.18 × 0.3= 0.054
8.5 ÷ 1.7= 5
1.2 ÷ 0.3 = 4
0.49 ÷ 0.7= 0.7
O .04 × 25=1
0.096 ÷ 0.03=3.2
84 ÷ 4.2= 20
1000 × 0.756=756
0.5 × 100= 50
2.5 × one point four seven × 0.4= 1.47
0 ÷ 0.25= 0
1 ÷ 0.01= 100
1.25 × 8=10
3.8 × 2= 7.6
7.2 ÷ 0.9=8
1.6 × 0.2= 0.32
9.3 ÷ 0.3= 31
4 ÷ 0.4=10
0.45 ÷ 0.5=0.9
0.2 ÷ 0.01 = 20
here is also the application of decimal division
1. A glass factory has to entrust a transportation company to transport 2000 pieces of glass, and the freight is 0.4 yuan per piece. If one piece is damaged, it needs to pay 7 yuan for the loss. As a result, the transportation company gets 711.2 yuan. How many pieces of damaged glass
200-711.2 = 88.8 (yuan) 7 + 0.4 = 7.4 (yuan) 88.8 ÷ 7.4 = 12 (blocks)
comprehensive formula: (200-711.2) ÷ 7 + 0.4) = 12 (pieces)
2. A classroom is 9 meters in length and 7 meters in width. How many tiles do you need to pave the floor with 0.6 meters in side length< br />9 x 7 ÷ 0.6 x 0.6
=63 ÷ 36 = 175 (pieces)
3. A taxi in a city starts at 2 km, and the starting price is 3 yuan. If it is more than 2 km, it costs 1.2 yuan per kilometer. Aunt Zhao takes a taxi from home to the park and pays 10.2 yuan when she gets off. How far is her home from the park
10.2 – 3 = 7.2 (yuan) 7.2 ÷ 1.2 = 6 (km) 2 + 6 = 8 (km)
comprehensive formula: (10.2 – 3) ÷ 1.2 + 2 = 8 (km)
4. An engineering team contracted the installation task of a water pipe. The original plan was to install 0.48 km per day, which was completed in 35 days. Actually, the installation was 0.6 km per day, how many days did it actually take< br />0.48 × thirty-five ÷ 6 = 28 (days)
5. There are 22 boys in a class, with an average height of 140.5cm; There are 18 girls with an average height of 142.5cm. What's the average height of the class< br />140.5 × 22+142.5 × 18 ÷ 22+18
=3091+2565 ÷ 40 = 141.4 (CM)
6. There are 10 grannies in the nursing home, with an average age of 80.5 years old; There are 12 grandfathers with an average age of 73.5 years. The average age of the elderly in the hospital was calculated. (the number obtained was kept to one decimal place)
(80.5) × 10+73.5 × 12 ÷( 10+12)
=(805+882) ÷ 22
≈ 76.7 years old

6. Divisor is the division of decimal, first move (divisor) decimal point, make it become (integer); Such as 0.756 ÷ 0.18=75.6 ÷ 18 = 4.2.
the decimal point of the divisor moves several places to the right, and the decimal point of the divisor also moves (several places to the right) (if there are not enough places, use "0" at the end of the divisor); Then calculate according to the decimal division with divisor (integer) ÷ 0.75=330 ÷ 75 = 4.4.
when dividing by integers, the decimal point of the quotient should be aligned with that of the divisor.
in the division formula, the quotient is written on the place where the divisor is divided. That is to say, the same digit of the divisor and the quotient is aligned. Only when the decimal point is aligned, the same digit is aligned, So the decimal point of the quotient should be aligned with the decimal point of the divisor

7. According to the nature of division, the divisor and divisor are expanded or reced at the same time, and the same multiple quotient remains unchanged. Rewrite the decimal into an integer, and then calculate according to the integer division.

8. 1 Strengthen ideological ecation, arouse students to enhance the desire to improve the accuracy rate of calculation. (2) let the law into the heart. (3) students often erase their calculation errors immediately after they find them. In order to make students have a correct learning attitude, I ask students to find out where the errors are and analyze the causes of the errors, For the decimal multiplication and division method, we often point the wrong decimal point. We should analyze whether we don't understand the arithmetic or because we don't master the method skillfully enough. If we don't understand the arithmetic, we should learn the corresponding knowledge. If we don't master the method skillfully enough, we should carry out special exercises (such as adding the decimal point to the vertical type). If we don't review the topic carefully, the handwriting is scribbled, Do not test and other bad habits, to develop good habits, calculation careful, patient, back to check after calculation

9.

I think you must have forgotten how to transform the decimal division.

there is a rule that if the numbers on both sides of the division sign are multiplied (divided) by the same number at the same time, the division result will not change

for example, 132 ÷ 1.1 can be changed into 1320 ÷ 11, multiply both sides by 10, and the result is the same

the same 1.32 ÷ 0.011 can be changed into 1320 ÷ 11, both sides multiplied by 1000

to 10.24 ÷ 016 as an example, the formulation will be deformed. I think you have already thought of it. Right, change the original formulation into 10240 ÷ 16

so it's easy to do

divide the decimal by the decimal (divisor and divisor are above zero)

divide the decimal by the decimal (divisor and divisor are below zero)

Divide the decimal by the decimal (divisor is below zero, divisor is above zero)

divide the decimal by the decimal (divisor is below zero, divisor is above zero), Pay attention to deformation

I made a picture myself, and now I send it to you