Find the volume of the cube, the sum of the lengths of all edges of which is equal to 30 dm

Decision:
1) Since the sum of the lengths of all the edges is 30 dm, and the cube has 12 in total, the length of one edge is: H = 30/12 = 2.5 (dm).
2) According to the formula, the volume of the cube is: V = H ^ 3, where V is the volume of the cube, H is the length of the edge of the cube.
V = (2.5) ^ 3 = 2.5 * 2.5 * 2.5 = 15.625 (dm ^ 3).
Answer: the volume of the cube is 15.625 dm ^ 3.