Here is the Formulae
This is usefull when the whole cube is painted with same color
All the Eight corners of the cube will have 3blacks
All the edges of the cube but look at extreme corners of the edge they have 3 blacks but we want 2 blacks hence we have to subtrace 2 from every edge and hence the formulae is (n-2) * 12
Here has it is given 125 means (5 * 5 * 5) hence n=2 i.e 3 * 12 = 36
Atleast 2 blacks means 2 or more blacks hence ==> 36 + 8 = 44 (answer)
Above answer was rated as good by the following members: rythm81, shrikant kh
Here is the Formulae This is usefull when the whole cube is painted with same color All the Eight corners of the cube will have 3blacks All the edges of the cube but look at extreme corners of the edge they have 3 blacks but we want 2 blacks hence we have to subtrace 2 from every edge and hence the formulae is (n-2) * 12 Here has it is given 125 means (5 * 5 * 5) hence n 2 i.e 3 * 12 36 Atleast 2 blacks means 2 or more blacks hence > 36 + 8 44 (answer)
RE: A cube is painted black. It is divided into 125 equal cubes. Find the number of cubes, which have at least 2 sides painted black?
8 cubes one at each corner of the cube will have 3 faces black. 3 cubes along each edge of the cube will have 2 faces black. There are 12 such edges & hence 12*3 36 cubes have 2 faces black. So total no of cubes having at least 2 faces black is 8+36 44 nos.
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