1. A cylinder with a bottom diameter of 10 cm and a height of 15 cm is cut into two and a half cylinders along the diameter 1. A cylinder with a diameter of 10cm at the bottom and a height of 15cm is cut into two half cylinders along the diameter. How many square centimeters does the surface area of the two half cylinders increase compared with that of the original cylinder? 2. A cylindrical oil barrel, full of oil, poured out 3 / 4 of the oil in the barrel, and there are 20 liters left. The height of the oil barrel is 8 decimeters. How many square decimeters is the bottom area of the oil barrel? 3. A cylindrical tank contains 10 cm deep water, and the bottom area of the tank is 300 square cm? 4. After sawing a 2-meter-long log into equal segments for three times, the surface area increases by 48 square centimeters. What is the original volume of the log?

1. A cylinder with a bottom diameter of 10 cm and a height of 15 cm is cut into two and a half cylinders along the diameter 1. A cylinder with a diameter of 10cm at the bottom and a height of 15cm is cut into two half cylinders along the diameter. How many square centimeters does the surface area of the two half cylinders increase compared with that of the original cylinder? 2. A cylindrical oil barrel, full of oil, poured out 3 / 4 of the oil in the barrel, and there are 20 liters left. The height of the oil barrel is 8 decimeters. How many square decimeters is the bottom area of the oil barrel? 3. A cylindrical tank contains 10 cm deep water, and the bottom area of the tank is 300 square cm? 4. After sawing a 2-meter-long log into equal segments for three times, the surface area increases by 48 square centimeters. What is the original volume of the log?

1.10 * 15 * 2 = 300 square centimeter
20 divided by 1 / 4 = cylinder volume = 80 cubic decimeter. 80 divided by 8, the bottom area of the cylinder is 10
3. First find the volume of cube, 6 * 6 * 6 = 216 cubic centimeter. Then divide 216 by 300, it is equal to 0.72 centimeter

The diameter of the bottom surface of a cylinder is 10 cm and the height is 6 cm. Cut it into two equal half cylinders. The sum of the surface areas of the two half cylinders is larger than that of the original cylinder

10 times 6 = 60cm 60 times 2 = 120cm

The side length of the two bottom surfaces of a regular triangular pyramid is 30cm and 20cm respectively, and the side area is equal to the sum of the two bottom areas

Area of top and bottom = √ 3 / 4 (30 ^ 2 + 20 ^ 2) = 325 √ 3 = side area = 3 trapezoidal area
Ψ trapezoid area = (30 + 20) H / 2 = 25h = 325 √ 3 / 3
The height of trapezoid H = 13 √ 3 / 3
Height of pyramid H = √ {H ^ 2 - [(5 √ 3-10 √ 3 / 3) ^ 2} = 4 √ 3