Problem 55 worked answer

Steve’s Chestful Challenge

Designed for Grade 5 · Uses Middle Grade 5 math · About 7–18 minutes

Complete to collectMarble TabletLevel 3

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 volumeEmpty inner volumeVault usesBlocks left
1,7281,0007281,000

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

MJ 5.5 · C3 · W2 Stretch challenge · Moderate workload

Measurement and units · Operations and computation

How the rating works →

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