Question: How many additional blocks are required to make the cube whole? (Assume the hidden inside cubes are there.)
Answer: The answer is 45.
The block in the picture has a height of 4 cubes and a width and depth of 5 cubes. So in order to create a “cube”, you would need to add a 5×5 cube to the top or bottom, in addition to filling in the blank spaces.
You’ll need 20 cubes to fill in the blank spaces. Creating a new 5×5 cube, you need 25 additional cubes.
20 + 25 = 45.
You’ll need 45 cubes total to create a cube that’s whole.