There were a reasonable number of people at the community meeting.

reasonable 由 reason（理由）加后缀 -able（能够...的）构成，字面意思是"有理由的"，引申为"合理的、适度的"。 reasonable number 表示"合理的数量"，指数量既不太多也不太少，在具体语境中可以理解为"相当数量的"。