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ASVAB · Simple Machines (Levers, Pulleys, Gears)

A small gear with 10 teeth drives a large gear with 40 teeth. If the small gear rotates at 200 RPM, what is the large gear's speed?

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Correct answer

50 RPM

  1. A 50 RPM
  2. B 800 RPM
  3. C 100 RPM
  4. D 25 RPM

Why this is the answer

Gear ratio = driver teeth / driven teeth = 10/40 = 1/4. Large gear speed = 200 × (10/40) = 200 × 0.25 = 50 RPM. When a small gear drives a larger one, the larger gear turns more slowly but with more torque — speed and tooth count are inversely related. Each turn of the 10-tooth gear advances the 40-tooth gear by only a quarter turn, so 200 RPM becomes 50 RPM. The distractor 800 RPM applies the ratio backwards (that would be the result if the 40-tooth gear were driving), 100 RPM halves instead of quartering, and 25 RPM uses a ratio of 1/8.
Source: ASVAB MC, Gears

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About this topic: Simple Machines (Levers, Pulleys, Gears)

Simple machines — levers, pulleys, gears, inclined planes, wheel-and-axle, screws — are the heart of Mechanical Comprehension. Each question comes down to mechanical advantage: how much the machine multiplies force, and the trade-off in distance. This is one of 23 Mechanical Comprehension questions on simple machines (levers, pulleys, gears), each with a full explanation on a single study page.

New to this exam? Our ASVAB exam guide explains the format, scoring, and how to prepare.

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