Answer:
What is the gear ratio
The gear ratio is the ratio of the number of teeth in the gear to the number of teeth in the pinion, the pinion being the smaller of the two gears in mesh.
What is the great reduction
reduction refers to the rewriting of an expression into a simpler form
what is the simplified gear reduction
If you count up the number of teeth on gear one, and on gear X (the last one) and set them in a ratio (1:X), this is the gear ratio. If the number can be reduced, you should reduce it, for example a ratio of 100 teeth:40 teeth reduces to 5:2