A big cube is formed by rearranging the 160 coloured and 56 non-coloured similar cubes in such a way that the expouser of the coloured cubes to the outside is minimum. The percentage of exposed area that is coloured is:

Total number of cubes = 160 + 56 = 216
Thus, side of cube = 6 unit
No. of cubes without exposure = (6 - 2)³ = 64
Thus 64 cubes will be inside of a big cube
Now, rest cubes = 160 - 64 = 96
No. of cubes with one face outside = 6 × (4 × 4) = 96
Required % = $$\frac{{90 \times 100}}{{216}} = 44.44\% $$