Bicycles and Rotational Motion

[Soaring Crane]

How is the angular speed of the rear wheel (w_R) of a bicycle related to that of the pedals and front sprocket (w_F) ?

To show this relationship, I have to derive a formula for w_R/w_F. N_F and N_R are the number of teeth on the front and rear sprockets , respectively. The teeth are spaced equally on all sprockets so that the chain meshes properly.

Please help me start up the problem. Thanks for any pointers.

[Galileo]

The idea is that the number of 'teeth' passing through a certain point for a given time interval is the same for both sprockets.
So if the front sprocket has twice as many teeth as the rear one, the rear sprocket will
rotate twice as fast as the front one.