Example 2:[ Choose] There are more students in Class A than Class B, so there are fewer students in Class B than Class A ().

A, B, C,

Example 3: A batch of 2520 parts, several parts are processed in the first week, and all parts are processed in the second week. At this time, the number of machined and unprocessed parts is the same. How many parts are processed in the first week?

Example 4: In a math contest, some students won the first prize, the second prize and the third prize. It is understood that less than 50 students participated in this competition. How many students won the first prize, second prize and third prize?

Example 5 Xiaohong bought a bag of rice, weighing 40 kilograms. How many catties are left after eating?

Example 6 Xiaohong bought a bag of rice and ate it, leaving 15 Jin. How many kilograms of rice did you buy?

There are five male workers and eight female workers in a workshop. What is the ratio of male workers to female workers? How many times the number of female workers is that of male workers?

According to the number of students in three classes of grade six, the school assigned each class the task of planting 280 trees. There are 47 students in Class One, 45 students in Class Two and 48 students in Class Three. How many trees should be planted in each of the three classes?

Example 9 Application of One-step Fraction

Uncle Zhang keeps 200 geese and 500 ducks. What are the numbers of geese and ducks?

Uncle Zhang has raised 200 geese, the number of which is only the number of ducks. How many geese does he have?

Uncle Zhang keeps 200 geese, and the number of ducks is only the number of geese. How many ducks does he have?

Example 10 ① The waterway length from Shanghai to Hankou is1125km. A ship has traveled three-fifths of the way from Shanghai to Hankou. How many kilometers is it from Hankou?

(2) A ship from Shanghai to Hankou is 450 kilometers away from Hankou. How many kilometers is the waterway from Shanghai to Hankou?

Example 1 1 Display problem group:

① There are 8 buses in the parking lot, which are more than buses 1/6. How many cars are there?

② There are 8 buses in the parking lot. There are fewer buses than cars 1/7. How many cars are there?

③ There are 2/kloc-0 cars in the parking lot, and there are fewer buses than cars 1/7. How many buses are there?

④ There are 2 1 car in the parking lot. There are more cars than buses 1/6. How many buses are there?

Example 12, fill in the blanks

(1) In the same circle, the ratio of diameter to radius is ().

(2) Spread the legs of the compass 4 cm and draw a circle with a diameter of ().

(3) Draw the largest circle in a square, and you can find the diameter of the circle and the side length of the square.

Example 13. A semicircular flower bed with a diameter of12m is planned to be surrounded by a circle of iron railings. How long will the iron railing be surrounded?

Example 14. What is the circumference of the shaded part in the picture below?

6 decimeters

8 decimeters

Example: warehouse a has 100 tons of grain, and warehouse b has 80 tons of grain. How many tons are taken out of warehouse A and put into warehouse B, which will make the grain tonnage ratio of warehouse A and warehouse B 7: 1 1?

Example 16. Show a supplementary example: a circular pool with a circumference of 37.68 meters. What is its diameter?

Example 17 Bend an iron bar with a length of 1.2m into a circular iron ring. What is the radius of this iron ring? (Figures shall be kept to two decimal places)

Example 18 A rope with a length of 47. 1 m is exactly three times around a circular stake. What is the radius of this circular stake?

Example 19 If a wire is bent into a circle, a circle with a radius of 4 decimeters can be obtained. If this line is used to form a square, what is the area of the square? (Numbers are reserved to one decimal place)

If you bend a wire into a semicircle, you can get a circle with a radius of 4 decimeters. If this line is used to form a square, what is the area of the square? (Numbers are reserved to one decimal place)

Example 2 1 The circumference of the semicircular fish pond below is 51.4m. What is its radius?

Example 22 Find the length of the runway in the next lap: (unit: meter)

There are two pulleys connected together. The big pulley has a diameter of 72 cm and the small pulley has a diameter of 24 cm. If the big wheel turns once, how many times will the small wheel turn? The first network of new curriculum standards

Example 25 Find the perimeter of the following figure (unit: cm)