Also thanks to Snakey. Longer method but same answers

To determine the engine to rear wheel gear ratio, do you just divide the teeth on the large driven sprocket by the teeth on the drive sprocket? I am proposing to install the engine in the front and use a single layshaft somewhere along the side with driver and driven sprockets of different sizes. I am using this arrangement for two reasons, one, to shorten the chain length and two, so ratio change is made easy by changing the driving sprocket on the layshaft to the rear wheel. Therefore I need to make two calculations, engine to layshaft and layshaft to rear wheel. Do I just add the two results together or is there more to it than that? 

Hi Stefan
I am new member JNS who lives Hythe Kent. I intend to attend the meeting but what is the address in Kingsley.