Error-prone situation:
Mother bought a desk lamp from 52 yuan.
(1) If 10 yuan is written by her mother, she should at least write () 10 yuan.
(2) If my mother has just enough money to buy this desk lamp, she can bring at most () 10 yuan.
Error cause analysis:
Question 1: Students may be influenced by the composition of numbers. Are there 5 10 and 2 1 in 52 that ignore the given condition? Mom paid 10 yuan? That is, mom can't have change, but she filled in at least five pieces by mistake; Question 2: Students may ignore the given conditions? Just right? And then what? Most? That is to say, except for 2 yuan, everything else is 10 yuan, but if you fill it wrong, you will have to pay 6 yuan at most.
Think about solving problems:
Children look at the problem carefully, and you will find that the two problems are different: the first question (1), mom has handed in all 10 yuan, and there is no change, so at least 6 10 yuan is enough. Question (2): My mother brought just enough money to buy this desk lamp, which proves that the money she brought was 52 yuan, so she brought at most five 10 yuan.
Problem solving process:
(1) Pay at least (6) pieces 10 yuan.
(2) At most, I brought (5) 10 RMB.
Variant correction:
Miss Li bought a football from 48 yuan.
(1) If all Mr. Li has paid is 10 yuan, he should at least pay () 10 yuan.
(2) If Mr. Li happens to have enough money to buy this football, he has at most () 10 yuan.
Summary of common error-prone cases:
1, every three balls are packed in 1 box. How many boxes do you need to hold 17 ball?
17? 3=5 (box) 2 (piece)
Error analysis: If there is any problem with the remainder, students are advised to install it in kind.
2. Xiaojun shot 3 1 time, and Xiaoli shot 20 times less than Xiaojun's 3 times. How many times did Xiaoli take pictures?
3 1? 3=93 (bottom)
93+20= 1 13 (below)
Error analysis: the narrative mode of one more (one less) is not suitable for students.
3. A bundle of wires walks 68 meters in the morning and 76 meters in the afternoon, leaving 2 10 meters useless. How many meters is this bundle of wires shorter than the original one?
68+76= 144 (m)
2 10+ 144=354 (m)
Cause analysis: I didn't understand what the question asked, so the question was not solved. Students are advised to read the questions repeatedly and understand them.
4. Weld two 45 mm long iron bars into one, and the welding head is 5 mm. How long is the iron bar after welding?
45+45=90 mm
90-10 = 80mm
Cause analysis: Two 45 mm long iron bars are welded into one with only one welded joint.
5. A book has 278 pages. Xiao Ming read 55 pages on the first day and read 18 pages more on the second day than on the first day. How many pages have you read in two days?
55+ 18=73 (page)
278-73=205 (page)
Cause analysis: disturbance condition? 278? Influence, I didn't finish reading the questions I asked. Students should be told that the conditions of some questions have no practical use (interference conditions) and should be fully understood before making them.
6. The tree planting team planted 105 trees yesterday, and today it planted 28 fewer trees than yesterday. How many trees were planted in two days?
105-28=77 (tree)
Error analysis: The reading questions are incomplete. Students are advised to describe them briefly after reading the questions. Two conditions, one question? .
7. Fishing ground catches 504 fish in the morning, and catches fewer fish in the afternoon than in the morning 196. How many fish can this fish farm catch every day?
504- 196=308 (article)
Cause analysis: it belongs to the same kind of error as 16, and no intermediate problem will be found.
8. A batch of coal has transported 28 tons, and the rest is seven times as much. How many tons of raw coal?
28? 7= 196 (ton)
Cause analysis: it belongs to the same kind of error as 16, and no intermediate problem will be found.
9. Uncle Zhu walks 60 meters every minute. He walked from home for 5 minutes, 50 meters away from his work. How far does Uncle Zhu walk from home to work?
60? 5=300 meters
300-50=250 (meter)
Cause analysis: this problem is best understood by charts. When drawing a line segment, it is obvious to know whether to add or subtract.
10, a desk 62 yuan, more 34 yuan than a chair. How much is a set of tables and chairs?
62+34=96 (yuan)
96+62= 158 (yuan)
Error analysis: who is confused and who is less, can students let go? One more chair, 34 yuan? The front is complete. Read the questions again and again to find out who has the highest price.