The RPM of "A" is 100 and hobbed with 96 teeth. If gears "B", "C", and "D" have 80, 30, and 46 teeth respectively, the RPM of "D" in the gear train illustration is __________. See illustration MO-0088.
• Use the gear ratio formula: driver RPM × (driver teeth / driven teeth) for each mesh • Recognize that gears B and C are on the same shaft, so they turn at the same RPM • Overall train ratio is the product of the individual gear ratios between A→B and C→D
• First, compute the RPM of gear B using the given RPM and teeth of gear A and the teeth of gear B • Then apply that same RPM to gear C (since it is rigid with B) to find the RPM of gear D using their tooth counts • Compare your final computed RPM for D with the choices and think about whether the speed should go up or down at each stage
• Be sure you always put driver teeth in the numerator and driven teeth in the denominator when finding the new RPM • Confirm that you do two separate calculations: one from A to B, and one from C to D • Double‑check that you did not directly jump from A to D in a single step without using the compound gear (B–C) in the middle
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