Problem 23 · 2021 Math Kangaroo
Stretch
Spatial & Visual Reasoning
transformations
The picture shows 3 gears with a black gear tooth on each. Which picture shows the correct position of the black teeth after the small gear has turned a full turn clockwise?
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Answer: A
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Hint 1 of 2
Meshed gears turn in opposite directions; a full turn of the small gear moves the others by matching tooth counts.
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Hint 2 of 2
Track the black tooth on each gear after that rotation to find the consistent picture.
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Approach: rotate each meshed gear correctly
- When the small gear makes one full clockwise turn, the gears it meshes with rotate the other way by the same number of teeth.
- Following each black tooth to its new position, the arrangement that results is choice A.
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