Problem-Solving and Data AnalysisHardTurns of a driven gear
Problem-Solving and Data Analysis practice question
A gear with 12 teeth turns 5 full times, driving a second gear with 20 teeth. How many full turns does the second gear make?
Answer: 3
The teeth passing the contact point must match: 12 × 5 = 60 teeth. The 20-tooth gear turns 60/20 = 3 times.
Common wrong answers
- If you answered 5
- 5 is the first gear's turns; the second gear is larger, so it turns less.
- If you answered 8.33
- 8.33 is 5 × 20/12, scaling the wrong way; the larger gear turns FEWER times.
- If you answered 1.67
- 1.67 is 20/12, the tooth ratio, not the number of turns.
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