Problem 55 worked answer
Steve’s Chestful Challenge
Designed for Grade 5 · Uses Middle Grade 5 math · About 7–18 minutes
At a glance
- Part 1: The chest and the solid cube each contain 1,728 cobblestone blocks. Steve is correct.
- Part 2: The hollow vault uses 728 blocks, leaving 1,000 blocks.
- Part 3: The leftovers make 15 full stacks with 40 extra blocks.
1. Prove the two models match
Page 1: chest total
A single chest has 27 slots, and every full stack contains 64 cobblestone:
.
Page 2: cube volume
The claimed solid cube has volume
cubic blocks.
The totals match, so Steve’s claim is correct.
The side length also follows directly from the arrangement. Each stack-cube is 4 blocks long, 4 blocks wide, and 4 blocks high. Steve places 3 stack-cubes along each direction, so each side of the large cube is blocks. The full array contains stack-cubes, with no gaps and no blocks left over.
2. Build the hollow vault
The outside volume is
blocks.
Because the walls are 1 block thick on opposite sides, the empty inside measures blocks in every direction. Its volume is
blocks.
The vault’s cobblestone shell uses
blocks.
Starting from the 1,728-block chestful leaves
blocks.
| Outer volume | Empty inner volume | Vault uses | Blocks left |
|---|---|---|---|
| 1,728 | 1,000 | 728 | 1,000 |
3. Restack the leftovers
remainder .
So the leftovers make 15 full stacks and 40 extra blocks.
Check
- and .
- , so the shell and empty inside reconstruct the outer cube.
- , so the stack-and-remainder result reconstructs the leftovers.
Common errors
- Treating 27 as a one-dimensional row instead of stack-cubes.
- Multiplying for the large cube’s side length. Only 3 stack-cubes lie along each direction, so the side length is .
- Subtracting only 1 from 12 for the inside dimension. A one-block wall is removed from both ends of each dimension, giving .
- Reporting 15 remainder 40 without naming 15 full stacks and 40 extra blocks.
Technical fit and rating
Measurement and units · Operations and computation
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