Finally you may find the word 'person' attached to a number. For example 'a two-person car', 'a three-person room'. This is where 'person' is being used to describe the noun. '2 – person' is the adjective describing 'car' and as you know we don't put an 's' on an adjective. So far example we talk about a 'two-week holiday' not a 'two-weeks holiday' or a 'three-year course' not 'a three-years course'. So hear we use 'two-person car'.