Maths Olympiad Prep

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Combinatorics Difficulty 6.4 National olympiad Find the answer

Is it possible to build a 4×4×4 4\times 4\times4 cube from blocks of the following shape consisting of 4 4 unit cubes?

Solution

To determine if it is possible to build a 4×4×44 \times 4 \times 4 cube from blocks consisting of 4 unit cubes, we need to consider the following:

1. Volume Calculation:
- The volume of the 4×4×44 \times 4 \times 4 cube is:
4×4×4=64 unit cubes 4 \times 4 \times 4 = 64 \text{ unit cubes}
- Each block consists of 4 unit cubes. Therefore, the number of such blocks needed to fill the 4×4×44 \times 4 \times 4 cube is:
644=16 blocks \frac{64}{4} = 16 \text{ blocks}

2. Shape and Tiling:
- We need to ensure that the blocks can be arranged to completely fill the 4×4×44 \times 4 \times 4 cube without any gaps or overlaps.
- The problem does not specify the exact shape of the blocks, but we can assume they are tetrominoes (shapes made of 4 unit cubes).

3. Parity Consideration:
- A 4×4×44 \times 4 \times 4 cube has an even number of unit cubes along each dimension.
- Each block consists of 4 unit cubes, which is also an even number.
- Since both the cube and the blocks have even dimensions, it is possible to arrange the blocks to fill the cube without violating parity constraints.

4. Constructive Approach:
- One way to visualize the construction is to consider the 4×4×44 \times 4 \times 4 cube as composed of smaller 2×2×22 \times 2 \times 2 sub-cubes.
- Each 2×2×22 \times 2 \times 2 sub-cube contains 8 unit cubes, which can be filled by 2 blocks of 4 unit cubes each.
- By arranging the blocks within each 2×2×22 \times 2 \times 2 sub-cube and ensuring that the blocks fit together across the boundaries of these sub-cubes, we can fill the entire 4×4×44 \times 4 \times 4 cube.

5. Conclusion:
- Given that the volume and parity constraints are satisfied, and that it is possible to arrange the blocks within smaller sub-cubes, it is indeed possible to build a 4×4×44 \times 4 \times 4 cube from blocks consisting of 4 unit cubes.

The final answer is True

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.