The sum of the lengths of all the edges of a rectangular parallelepiped is 28cm.

The sum of the lengths of all the edges of a rectangular parallelepiped is 28cm. Find the sum of the lengths of its three edges going out from one vertex.

We argue as follows:

1) A rectangular parallelepiped has four equal heights, four equal lengths and four equal widths. Thus, a rectangular parallelepiped has four identical sets of edges emanating from one vertex: height, length, and width.

2) Then, in order to find the sum of the lengths of three edges of a rectangular parallelepiped outgoing from one vertex, you need to divide the sum of the lengths of all edges by four.

28: 4 = 7 (cm);

Answer: 7 cm.