125 = 5³ = 5 · 5 · 5
Every side of a larger cube is cut into 25 congruent squares.
Number of sides of smaller cubes that are painted: 25 · 6 = 150
Number of all sides of 125 cubes: 125 · 6 = 750
Probability : P(A) = 150/750 = 1/5 = 0.2
Answer: probability is 0.2 or 20%