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1. The cross section of a cement pipe is annular, the diameter of the inner circle is 30 cm, and the radius of the outer circle is 20 cm? 2. A rectangular cardboard, 1.6 decimeters long, 8 cm wide, cut diameter is 4 cm circle, how many can cut at most? 3. The outer diameter of the train wheel is 0.8 meters. If it turns 400 circles per minute, how many kilometers does the train advance per hour? 4. Ten granaries with circular bottom will be built in the western suburbs. The perimeter of each granary bottom is 9.42 meters. What is the total area of the granary? 5. There are 150 cases of apples and pears in total, of which apples are half more than pears. How many cases of pears and pears are there? 6. The distance between a and B is 360 km. A bus and a train depart from the two places at the same time and meet each other in 4 hours. The speed ratio of the bus and the train is 5:4. What is the speed of the bus and the train?
1. (20-15) 2 × 3.14 = 78.5 square centimeter
2. (16 / 4) × (8 / 4) = 8
3. 0.8 × 2 × 3.14 × 400 × 60 = 120576 (m) = 120.576 (km)
4. 2 × 3.14 × 15 = 105.975 (M2)
5. If there are x boxes for apples, there are (150-x) boxes for pears
X－(150－X)=0.5X
The solution is x = 100 150-100 = 50 cases
There are 100 cases of apples and 50 cases of pears
6. If the speed of the bus is x, the speed of the train is 4 / 5x
(X+4/5X) ×4=360
The solution is x = 50 km / h, 50 × 4 / 5 = 40 km / h
That is, the speed of the bus is 50 km / h and 50 km / h
The speed of the train is 40 km / h
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