Direction: 343 Small unpainted cubes are arranged to from a large cube. All the six faces of the large cube are painted white. Now, a 3 x 3 cube, comprising 27 small cubes, is removed out from one of the corners of the large cube. The 3 x 3 cubes is now painted blue on all six faces, while all the three surface (each of which a is a 3 x 3 square) of the large cube exposed due to the removal of the 3 x 3 cube are painted black. Then, the 3 x 3 cube is put back in its original position in the large cube and the large cube is finally painted yellow on all the six faces.
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What is the number of small cubes which have exactly three faces painted?
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- 8
- 16
- 18
- 19
Correct Option: C
Initial total number of cubes = 343,
Number of cubes removed = 27
Smaller 27 cubes painted blue
Exposed faces of original big cube (3 faces with 9 cube on each face i.e total 27 cubes) painted with black
Since 7 corner (Vertices) of bigger cube is untouched hence they are painted with three faces.
Now consider the corner from where we have removed 3 x 3 x 3 cubes,
After removed 3 new corners of the bigger cube will be generated that will be painted with 3 faces and 8 corners from smaller cube of 3 x 3 x 3 painted with 3 faces.
So the such total number of such cubes is 7 + 3 + 8 = 18.
