This result accounts for the use of the word paradox to describe this train. Not only do we get a much larger ratio (100:1) than we could from a conventional train with gear of 100 and 20 teeth, but we have our choice of output directions!
Automotive automatic transmissions use compound planetary rains, which are always in mesh, and which give dethrone ratio forward speeds, Plus reverse, by simply engaging and disengaging brakes on different members of tire train. The brake provides zero velocity input to one train member. The other input is from the engine. The output is thus modified by the application of these internal brakes in the transmission according to the Selection of the operator