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Some math problems, 3Q 1. A rectangular ventilation pipe, 4 meters long, with a cross section of 80 cm square. How many square meters of iron sheet is needed to make 100 such ventilation pipes? 2. There are two cubes whose edges are both 15 cm long. Put them together into a cuboid. The surface area of the cuboid is less than the sum of the original two cubes () 3. The total length of the edges of a cuboid is 80 cm, the length is 10 cm, the width is 7 cm, and the height is () cm
(1) 4 * (80 / 100) * 100 = 320 square meters answer: to make 100 such ventilation pipes, it needs at least 320 square meters of iron sheet. (2) there are two cubes with the length of 15 cm, and they are put together into a cuboid. The surface area of the cuboid is less than the sum of the original two cubes (450 square centimeters) (3) one
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