A solid red coloured cube is painted yellow on all sides. The cube is cut into 125 equal cubes. How many sides will have 3 sides yellow?

We follow the given pattern :-
In Layer-I, the nine central cubes have only one face painted, four cubes at the corner have three faces painted and the remaining 12 cubes have two faces painted.
In each of the Layer-II, III and IV, the nine central cubes have no face painted, the four cubes at the corner have two faces painted and the remaining 12 cubes have one face painted.
In Layer-V, the nine central cubes have only one face painted, the four cubes at the corner have three faces painted and the remaining 12 cubes have two faces painted.
Thus, the number of cubes having three faces painted = 4 + 4 = 8