First find the radius of the cylinder: 62.8 ÷ 3. 14 ÷ 2 = 10 cm.
Find the bottom area of a cuboid: 10 squared+10 squared = 200 square centimeters.
Volume of cuboid: 200× 30 = 6000 square centimeters.
Volume of cylinder: 10 square× 3.14× 30 = 9420 square centimeters.
Volume of cut-off part: 9420-6000 = 3420 cm2.
1.5m = 15 decimeter
The reduction of surface area actually reduces the side area of the sawed cylinder, and the circumference of the bottom surface can be found: 50.24 ÷ 4 = 12.56 decimeter.
12.56 ÷ 3.4 1 ÷ 2 = 2 decimeters This is the bottom radius.
Wood volume: 2× 2× 3.14×15 =188.4 cubic decimeter.
The third question can also be understood in this way.
The radius of the cylinder bottom is 62.8/3.14 * 2 =10cm. When calculating the largest cuboid after machining, the bottom of the cuboid should be square.
10 * 2 = 20cm
20 * 10/2 * 2 = 200 square centimeters
200 * 30 = 6000 square centimeters is the volume of a cuboid.
10 *10 * 3.14 * 30 = 9420 cm2.
9420-6000 = 3420 square centimeters