1. A cylinder with a bottom radius of 5cm and a height of 8cm, divide its bottom into many equal sectors and cut it into an approximate cuboid. How much larger is the surface area of this cuboid than that of a cylinder?

Increase: 5×2×8=80cm?

There is a cylindrical glass cylinder with a bottom diameter of 2 decimeters, and there is no water in it. Put an iron ball in it. When the iron ball completely sinks into the water and the water level rises by 3 cm, find the volume of the iron ball.

The volume of the ball =(2÷2)? ×3. 14×3=9.42cm？ ;

3. Enclose a cylindrical grain depot with a piece of iron sheet with a length of 28.26 meters and a width of 4 meters (joints are ignored). What is the volume of this grain depot?

Maximum bottom radius = 28.26. 3. 14÷2 = 4.5m；

Volume =4.5? ×3. 14×4=364.5m？ ;

4. The bottom radius of the cylindrical barrel is 20cm. After taking out a small stone from the bucket (the stone is completely immersed in water), the water in the bucket drops 1cm. What is the volume of this small stone?

Stone volume =20? ×3. 14× 1 = 1256cm？