Problem 12 · 2015 Math Kangaroo
Medium
Spatial & Visual Reasoning
cube-viewscareful-counting
Every one of these six building blocks consists of 5 little cubes. The little cubes are either white or grey. Cubes of equal colour don’t touch each other. How many little white cubes are there in total?
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Answer: C — 12
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Hint 1 of 2
In each block of 5 cubes the colours alternate, so they go grey-white-grey-white-grey.
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Hint 2 of 2
Count the white cubes in one block, then multiply by the number of blocks.
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Approach: count white per block, then scale to all blocks
- Because same-colour cubes never touch, each block of 5 alternates colour, giving 3 of one colour and 2 of the other.
- Each block ends up with 2 white cubes.
- With 6 blocks that is 6 x 2 = 12 white cubes, choice C.
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