A quick search reveals that dictionaries are inconsistent in defining "most." The relevant definition that is indicated in many of them is "a majority of," or some equivalent words. Some, however, indicate "a great majority" or "nearly all."
Even if we grant the contention by Joe (Trelja) that "0 is not one of the endpoints," which is debatable IMO, but if we accept the "majority of" definition, Ralph's statement comes within an infinitesimally small increment of being correct (for example, 40.000000001 encompasses a majority of the difference between 20 and 60). In which case claiming that Ralph is wrong because 40 does not encompass a majority of that difference would seem to be splitting hairs, as he indicated.
On the other hand, using the "great majority of" or "nearly all" definitions, Ralph's statement would be incorrect, certainly if the lower endpoint is considered to be 20, and probably even if 0 is considered to be that endpoint.
The bottom line, IMO: It's listener dependent :-)
Best regards,
-- Al