Okay, done some more research and thought about the problem...
If eve=the eavesdropper, bob and alice= the people trying to communicate
the publicly shared number is 120
bob chooses a random number(4) computes 120/his number (30) and publicly sends this to alice,(eve also gets it)
alice does the same as bob using 6
the number bob received/the number he used to divide 120=5
alice does the same and gets 5
eve cannot make 5 from combinations of her numbers


can someone please tell me if this is a fluke, if there are problems with it or if it would work?