The volume of the large cube is 5³ = 125 cm³. The volume of each small cube is 1³ = 1 cm³. The number of small cubes is the total volume divided by the volume of each small cube: 125 cm³ / 1 cm³ = 125 cubes. The surface area of the large cube is 6 × side² = 6 × 5² = 6 × 25 = 150 cm². The surface area of one small cube is 6 × side² = 6 × 1² = 6 cm². The sum of the surface areas of all the smaller cubes is the number of small cubes multiplied by the surface area of one small cube: 125 × 6 = 750 cm².