In a compound gear train, Gear A (driving gear on motor shaft) has 20 teeth and rotates at 1000 rpm. It meshes with Gear B (40 teeth). Gear C (20 teeth) is mounted on the same shaft as B and meshes with Gear D (40 teeth). Gear E (20 teeth) is on the same shaft as D and meshes with Gear F (100 teeth) on the output shaft. Determine the speed ratio (ratio of driver speed to follower speed) of this gear train.

In the differential gear of a car, the pinion mounted on the propeller shaft has 20 teeth and the crown gear has 100 teeth. The propeller shaft rotates at 600 rpm. When the vehicle is taking a turn, one wheel rotates at 140 rpm. Determine the percentage change in speed of the other wheel.

A rack-pinion system has a pinion with 24 involute teeth, 144 mm pitch circle diameter, addendum of 6 mm for both pinion and rack, and 20° pressure angle. Calculate the contact ratio of the rack and pinion mechanism.