What is the difference between a 88 key piano and a 73 key piano?

Question

And if I knew how to play a 88 key piano would I have to learn have to play a 73 key piano.

Answer 1

The part you mostly play is identical.  The shorter keyboard is missing about half an octave at the top and at the bottom where most songs do not involve playing.  If you do songs that extend to the very end of 88 key unit, then you will have problems with the shorter.   Also short bad for 4 handed duets on one piano.