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7 years, 9 months ago
7 years, 8 months ago
The cut will go through a total of 49 cubes (Imagine a cube with 7 layers of 7*7 cubes, and a cut going along a diagonal of all these layers. Among these 49 cubes, 7 cubes in top and bottom layer would be colored. Also, for the cubes along the edges (7+7) will be colored. Since we have already considered the top and bottom layer edges cube twice we would remove them. So total number of cubes which were colored but were cut= 24(14+14-4). Units cubes which were not painted but cut=49-24=25