Primary school mathematics is an important period for us to divergent thinking. Now I have prepared a wrong summary of primary school mathematics for you, hoping to help you!
1. When calculating in the form of a column, you must pay attention to the difference between division and division: A divided by B or A divided by B. The form of the column is: A? B, a divided by b, or a divided by b, the formula is: b? a
2. A square with a side length of 100px and a circle with a radius of 50px have different areas and perimeters, so they cannot be compared! Should be expressed as:? Is the perimeter and area of a square with a side length of 100px equal? .
There is a difference between the circumference of a half circle and that of a half circle.
4. How many meters does the roller advance at a time? Is to find its circumference. The road surface area rolled by the roller in a cycle is the lateral area of the roller.
5, uncovered buckets, pools, goldfish bowls, sinks, etc. When seeking surface area, the bottom area must be reduced.
6. How much is a large number larger than a decimal? Decimal)? Unit? 1? The number of.
7. Two ropes of the same length, one cuts the rice, the other cuts the rice, and the remaining lengths cannot be compared; A rope is cut into two sections, the first section is meters long, and the second section is not unparalleled, but the first section is long.
8、0.52? The quotient of 0. 17 is 3, and the remainder is 0.0 1 instead of 1.
9. In the formula for finding the rate or percentage, it must be 100? .
10, when solving the application problems of the total number of people and the total number of trees, the results cannot be fractions and decimals.
1 1, rewrite an accurate number, no need? Rounding? When taking an approximation, be sure to put? Wan? Or? Billion? The following figures are written to the decimal part; Only about or omitted? Wan? Or? Billion? When the mantissa after the bit is used. Rounding? Do you have to write the approximate end? Wan? Or? Billion?
12, reading large numbers: the problem of reading several zeros
Related example10,0070,0008 How many zeros did you read?
Other answers are wrong
2 correct answers
Reading large numbers with examples is a knowledge point in grade four, especially reading a few zeros, which is easy to make mistakes.
13, approximation problem
The approximate value of a number is 10000, and the maximum number is _ _ _ _ _ _ _.
Wrong answer 9999
Correct answer 14999
The approximate value obtained by example rounding may be more than? Five inches? You got it, maybe? Four houses? I see.
14, numerical size sorting problem: pay attention to the size order required by the topic.
For related examples, put 3. 14,? , 22/7 _ _ _ _ _ _, in descending order.
Wrong answer 3. 14
Correct answer 22/7 & gt；; ? & gt3. 14
Example evaluation questions are on call, don't be silly. And be sure to write the original number sorting.
15. Scale problem: pay attention to the scale of the area.
Related examples On the sand table with the scale of 1: 2000, the ecological park with an actual area of 800,000 square meters is _ _ _ _ square meters.
Wrong answer 400
Correct answer 0.2
Example analysis Many students directly use 800,000 yuan? In 2000, I got the wrong answer. Remember, scale = distance on the map: the actual distance is the scale of the length, that is, the length unit of 1 on the map is actual.
2000 units of length. But this problem involves area and needs to be converted into the proportion of area. The ratio of square length is required, that is, the area unit of 1 on the drawing is the actual area unit of 4000000.
16, positive-negative ratio problem: the meaning of positive-negative ratio is not clear.
True or false: The area of a circle is proportional to its radius.
Wrong answer?
Correct answer?
Example analysis If the product of two quantities is a fixed value, it is inversely proportional; If the quotient of two quantities is a constant value, then it is proportional. Strict card definition, the original title changed to? Round. Is the area proportional to the square of the radius? , is correct.
17, comparison problem: pay attention to the order of the previous items.
Related examples After the side length of a square is increased by 1/3, the area ratio of the original square to the new square is _ _ _ _ _ _ _.
Wrong answer 16: 9
Correct answer 9: 16
When evaluating examples, you must keep your eyes open and see who is the first and who is the second!
18, the problem of ratio: the difference between ratio and ratio
Related examples After the side length of a square is increased by 1/3, the ratio of the area of the original square to that of the new square is _ _ _ _ _.
Wrong answer 9: 16
Correct answer 9/ 16
Example evaluation ratio is a result, not a number.
19. Unit problem: Don't leave out the unit.
The area of a square with a side length of 4 cm is _ _ _ _ _ _.
Wrong answer 16
The correct answer is 16 square centimeter.
The example evaluates the area problem, and the result is correct, but there is no unit to write it, just like a traveler in the desert, dying of thirst near the river. What a pity! Pathetic! Ridiculous! Alas!
20. Unit problem: Pay attention to the consistency of the unit.
Related examples A flour bag is marked with (25kg±50g), and the heaviest weight of this flour is _ _ _ _ _ _ _ _ kg.
Wrong answer 75
Correct answer 25.05
Example evaluation Many students did not see that the units of kg and G were inconsistent, and directly gave the wrong answer of 75.
2 1, leap year, flat year problem: the concept of leap year is unclear.
Related example 1900 is a leap year or a flat year?
Wrong answer leap year
The correct answer is the average year
Example analysis: jump in four years, not jump in a hundred years, and jump again in four hundred years. If a year is a multiple of 4, it is a leap year; Otherwise it will be a normal year. But if it is a whole hundred years (for example,1900,2000), then it must be a multiple of 400 to be considered as a leap year, otherwise it is a flat year.
22, solving the equation problem: the MINUS sign is in front of the brackets, and the number should be changed when the brackets are removed! Move the item to change the logo!
Related example 6? 2(2X？ 3)=4
Other answers are wrong
Correct answer x=2
Comment the example and remove the brackets. If there is a minus sign in front of the bracket, please change it! Move the item (a number moves left and right on both sides of the equal sign) to change the symbol, remember!
23. Calculation problem: Keep in mind the operation order.
Related example 20? 7? 1/7
Wrong answer 20
Correct answer 20/49
Example analysis 530 exams, calculation questions? Need technology? The trend is obvious. This paper focuses on the basic calculation skills such as the operation of four fractions, the operation sequence and the extraction of common factors.
24, the average speed problem
Related examples Xiaoming's uphill speed is 1 m/s and downhill speed is 3 m/s, so the average speed of Xiaoming's uphill and downhill is _ _ _
Wrong answer (1+3)? 2=2 (m/s)
The correct answer is that the whole journey up the mountain is 3 meters, and the average speed is: (3? 2)? (3? 1+3? 3)= 1.5 (m/s)
The definition of average speed is: total distance? total time
25. There are many topics.
Related examples The degree of an angle of an isosceles triangle is 50 degrees, so its vertex angle is _ _ _ _ _.
Wrong answer 80 degrees
The correct answer is 50 degrees or 80 degrees.
Examples comment on many types of topics, and the results are often more than one. Students must pay attention to the rigor of thinking, sum up more when doing problems at ordinary times, and try to take all the situations into account. Don't give an answer and think you're done.
26. Pay attention to the integrity of expression.
Related examples The ratio of three internal angles of a triangle is 1: 1: 2, which is a _ _ _ _ _ triangle.
The isosceles triangle answered incorrectly.
Correct answer isosceles right triangle
To evaluate this kind of questions with examples, only by thinking more and summarizing more in the usual training can we ensure that the exam will not be wrong.
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