Article 1 1, unit problem: Don't leave out the unit.
One side is 4 cm long and the area 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.
2. Unit problem: Pay attention to the consistency of the unit.
A flour bag is marked with (25kg plus or minus 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.
3. leap year and normal year: the concept of leap year is not clear.
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.
4, the average speed problem
Related examples Xiaoming's uphill speed is 1m/s and downhill speed is 3m/s, so Xiaoming's average downhill speed 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
5. Comparison of square area and perimeter
The area and perimeter of a square with a side length of 4cm are not! Item! Wait! Although the numerical results are all 16, because the units are different, 16 cm? 16 square centimeter, unparalleled.
6. The difference between division and division
A divided by b or a divided by b is: a? B, a divided by b, or a divided by b, the formula is: b? a
7. Matters needing attention in rewriting numbers
Rewrite an exact 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?
8. reading large numbers: read a few 0 questions.
Related example10,0070,0008 How many zeros did you read?
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.
9, avoid by all means half a person, half a tree
When solving the application problems of total number of people, total number of trees and total number of trees, the results cannot be fractions and decimals.
10, related calculation after the roller advances.
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.
Article 2 1 1, the circumference of a semicircle? Half the circumference
These two look the same, but they are actually different, because the circumference of a semicircle has an extra diameter.
12、? No cover? Easy to calculate? Is it covered?
When calculating the surface area of uncovered buckets, pools, goldfish bowls, sinks, etc. The bottom area must be reduced.
13, how much is a large number greater than a decimal?
(large number? Decimal)? Unit? 1? The number of.
14, rope length comparison problem
Two ropes with the same length, one cut off1/2m, and the other cut off1/2m, so the remaining lengths cannot be compared;
15, remainder quotient problem
0.52? The quotient of 0. 17 is 3, and the remainder is 0.0 1 instead of 1.
16, percentage related problem
In the formula of finding rate or percentage, it must be 100% in the end?
17, approximation problem
The approximate value of the related example integer is10,000, 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.
18, number 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.
19. 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 the actual length unit of 2000. 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.
20. Positive-negative ratio: 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? The area of a circle is proportional to the square of the radius? , is correct.
Chapter 3: 2 1, the problem of proportion: 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 obtained.
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!
22. The question 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 the area of the new square.
Wrong answer 9: 16
Correct answer 9/ 16
Example evaluation ratio is a result, not a number.
23, 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!
24. 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.
25. There are many topics.
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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