Subjects geometry

Painted Cubes

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Painted Cubes


1. **Stating the problem:** We have a composite 3D object made by combining identical small cubes. The object is dipped in red paint, then separated back into the small cubes. We need to find the number of small cubes obtained and answer related questions about the painted faces and arrangements. 2. **Formula and rules:** - The total number of small cubes in a rectangular prism is calculated by multiplying its dimensions: $\text{Total cubes} = l \times w \times h$. - When dipped in paint, only the outer faces of the cubes are painted. - The number of cubes with paint on exactly $k$ faces depends on their position: corner cubes have 3 painted faces, edge cubes have 2, face cubes have 1, and internal cubes have 0. 3. **Step 1: Calculate total small cubes (Question 01).** Assuming the composite object is a cube of size $5 \times 5 \times 5$ (from description 4), total cubes: $$5 \times 5 \times 5 = 125$$ 4. **Step 2: Number of small cubes with red paint on faces (Questions 02, 03, 04).** - Cubes with 3 painted faces (corners): 8 (each corner of the cube). - Cubes with 2 painted faces (edges excluding corners): $12 \times (5-2) = 12 \times 3 = 36$. - Cubes with 1 painted face (faces excluding edges): $6 \times (5-2)^2 = 6 \times 3^2 = 6 \times 9 = 54$. - Cubes with 0 painted faces (internal cubes): $(5-2)^3 = 3^3 = 27$. 5. **Step 3: Answering specific questions:** - Q02: Number of small cubes with 1 painted face ("five small consonants colored red" interpreted as cubes with one red face): 54. - Q03: Number of small cubes in a small triangle with four sides painted red (assuming a triangular arrangement with 4 painted sides): This is ambiguous without exact shape, but if referring to cubes with 3 painted faces (corners), answer is 8. - Q04: Number of faces of a small cube painted red: maximum is 3 (corner cubes). 6. **Step 4: Additional cubes needed to create a larger relief (Question 05).** If the current cube is $5 \times 5 \times 5 = 125$ cubes, and a larger relief requires, for example, $6 \times 6 \times 6 = 216$ cubes, then additional cubes needed: $$216 - 125 = 91$$ 7. **Summary of answers:** - Total small cubes after separation: 125. - Cubes with 1 painted face: 54. - Cubes with 3 painted faces (corners): 8. - Maximum painted faces on a small cube: 3. - Additional cubes needed for larger relief (assuming $6^3$): 91. **Final answers:** - 01: 125 - 02: 54 - 03: 8 - 04: 3 - 05: 91