example
A round table can seat 10 people. At Xiaoling's birthday party, she wants to sit with her good friend Feifei and let Feifei sit on her right. There are several different sitting postures.
10-2=8 (times)
8+ 1=9 (species)
Error cause analysis
Students think about this problem according to the law of normal graphic coverage. Use total number-coverage number = total number of translations, and translation number+1= to get several different sums. This question is a closed number, students can't understand the total clearly, so the translated number is wrong. Of course, several different sitting postures can't be calculated correctly.
The idea of solving the problem
A round table has 10 seats, and the seats are connected end to end. When translating to the ninth 10 seat, you can further translate to the 10 seat. The total should be considered as 10+ 1 instead of 10. If it is a three-person sitting method, the total should be 10+2, and the total should be 10+3, which is actually 1-65438.
Correct problem solving process:
10+ 1-2=9 (times)
9+ 1= 10 (species)
Variant correction
1. There are 10 chairs in the classroom, arranged in a row, with three people sitting together, A on the left, B in the middle and C on the right. How many different sitting positions are there?
There are 10 chairs in the classroom, arranged in a circle. A, B and C sit together. A should be on the left, B in the middle and C on the right. How many different seating methods are there?
3 1. Two teams completed a project in 12 days, while team A only took 20 days. How many days will Team B work alone?
32. The oil yield of rapeseed is 40%. How many Jin can rapeseed squeeze? How many kilograms of rapeseed does it take to squeeze 50 kilograms of oil?
33. A commodity is reduced by 10% first, and then increased by 10%. What's the percentage of the original price?
34. The original price of a story book is 9.6 yuan, and now it's 10% off. How much is each book now?
35. A*B=X*Y (four letters are not 0). Write eight different proportions.
36. To make a toy, A needs 6 points, B needs 5 points and C needs 7.5 points. Now the task of making 1500 toys is given to three people, and it is required to be completed at the same time. How much should everyone do?
37, two kinds of exercise books, one is 5 yuan 6, one is 3 yuan 4, the unit price ratio of these two kinds of exercise books is ().
38. The number of Class A is more than that of Class B 1/4, so the number of Class B is less than that of Class A ().
39. The radius of the bottom surface of the cylinder is enlarged by 3 times, the height is reduced by 3 times, and the volume is increased by () () times.
40. The distance of 1.5cm on the map indicates the actual 60km, so the numerical scale is () and the line segment scale is ().
4 1, the distance of 5 cm on the graph represents the actual 0.06 mm, then the numerical scale is ().
42. Two ropes of the same length, one was cut by 3/7 meters and the other by 3/7 meters, which one was cut for longer?
43. A rope is cut into two sections. The first section is 3/7 meters long, and the second section accounts for 3/7 of the total length. Which section is longer?
44. For the integer part, the fourth digit from the right is (), and the counting unit of the ninth digit is ().
45, the decimal part from the left, the first is (), the fourth counting unit is ().
46, the third counting unit to the right of the decimal point is ()
47,4: 32 = () (Fill in score)
48. A cylindrical piece of wood, 1.5m long, sawed into two parts along the bottom diameter, has an average surface area of 600 square centimeters. The volume of this kind of wood is () cubic centimeters.
49,3.25 hours = () hours () minutes
50, the height of the cylinder is certain, its bottom radius is proportional to the volume ().
There are 40 students in Class 2, Grade 6, 5 1, and 2 students are absent from class. The absenteeism rate is ().
52. The volume of a cylinder and a cone is equal, and the ratio of their heights is 1: 30, and the ratio of their bottom areas is ().
53. There are three steel pipes, each of which is 200 cm \240 cm and 360 cm long. Now, we want to cut these three steel pipes into as long and equal belts as possible. A * * *, how many sections? How long is each paragraph?
Make a cube with a side length of 1 cm with a side length of 1 decimeter. At least () pieces are needed, which are arranged in a row * * * and are () cm long.
55. Divide 5 kg of sugar into 8 portions, each portion accounts for ()/() of the total weight, each portion is 1 kg ()/(), and 5 kg accounts for ()/() of the total weight.
56. The approximate number of an integer in ten thousand is 50,000, and this number is (), and the smallest is ().
57.0. 1 ton: 50kg The simplest integer ratio is (): (), and the ratio is ().
58, a class attendance of 45 people today, there are three people ask for leave, today's attendance rate is ().
59. The height of a cylinder is 5 decimeters. Two square sections can be obtained by cutting along the diameter of the bottom surface. The circumference of the bottom of this cylinder is () decimeter.
60. The circumference of the cone bottom is 18.84 cm and the height is 6 cm. After cutting the cone in half along the height from the apex, the sum of the surface areas is increased by () square centimeters compared with the cone.