2. Zhang Wei bought 100 balls, of which red balls accounted for 28%, and the ratio of red balls to blue balls was 4:5. How many blue balls are there?

3. The circumference of the bottom of the uncovered cubic tin tank is 24 decimeters. How many liters of water can this tank hold? How many square decimetres does it take to make such a water tank?

The volume of a rectangular steel is 2800 cubic centimeters, and the cross section is a square with a side length of 10 centimeters. How many centimeters is the length of this steel?

5. A rectangular stone slope is 4 decimeters long, 3.5 decimeters wide and 2 decimeters thick. If this stone weighs 4.5 kilograms per cubic decimeter, how many kilograms does this stone weigh?

6. Pour 240 liters of water into a rectangular fish tank with a length of 10 decimeter, a width of 6 decimeters and a height of 8 decimeters. How deep is the water in the fish tank?

7. A conference room is15m long,12m wide and 4m high. How many square meters of floor tiles do you need to lay now? Paint its four walls and top surface, excluding 20 square meters of doors and windows. What is the area to be drawn?

8. A rectangular glass jar without a lid, viewed from the front, is 10 decimeter in length and 6 decimeters in height. Drain water in the cylinder, and the water surface is 3.2 decimeters away from the cylinder mouth. How many liters of water are there in the jar?

9. There are 8 steps in front of the school library, each of which is10m long, 0.4m wide and 0.3m high. (1) How many square meters does Babu * * * cover? (2) How many square meters of floor tiles should be laid on these steps?