Oilers/Plant Tenders (HHC) Civil Service Practice Exam

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If two gears have a gear ratio of 6 to 1, and the small gear rotates 120 revolutions per minute, how many revolutions does the large gear rotate?

60 rpm
20 rpm
30 rpm
10 rpm

The correct answer is: 20 rpm

To determine how many revolutions the large gear rotates, it's important to understand the relationship defined by the gear ratio. A gear ratio of 6 to 1 means that for every 6 revolutions of the small gear, the large gear will make 1 complete revolution. Given that the small gear is rotating at 120 revolutions per minute (rpm), we can calculate the speed of the large gear by dividing the speed of the small gear by the gear ratio. Since the ratio is 6 to 1, we take the 120 rpm of the small gear and divide it by 6: 120 rpm ÷ 6 = 20 rpm. This indicates that for every 120 revolutions of the smaller gear, the larger gear will complete 20 revolutions per minute. Thus, the large gear rotates at a speed of 20 rpm.