The RPM of "A" is 100 and hobbed with 72 teeth. If gears "B", "C", and "D" have 64, 24, and 36 teeth respectively, the RPM of "D" in the gear train illustration is __________. See illustration MO-0088.
• Relationship between gear speed (RPM) and number of teeth: (N_1 T_1 = N_2 T_2) for two meshing gears • How a compound gear works: gears mounted on the same shaft turn at the same RPM • Overall gear train ratio is the product of each mesh’s ratio (driver teeth / driven teeth)
• Which gear is directly driven by gear A, and which gear is mounted on the same shaft as that gear in the illustration? • Using (N_1 T_1 = N_2 T_2), what RPM do you get for the shaft that carries gears B and C when gear A (72 teeth) turns at 100 RPM and drives gear B (64 teeth)? • Once you know the RPM of gear C (same shaft as B), how does that speed change when C (24 teeth) drives gear D (36 teeth)?
• Be sure you are using the correct driver / driven pairing for each step (A→B, then C→D) based on the illustration, not guessing from the letters alone. • Double‑check that you carry the intermediate RPM from the A–B mesh forward as the RPM of both B and C (same shaft). • After computing the final RPM, confirm whether it is faster or slower than 100 RPM and eliminate any answer choices that don’t match that trend.
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