Hyphenated Adjectives

Remember that it is common for a number to appear as the first in a series of hyphenated adjectives. 

Each word in a hyphenated adjective is an adjective is an adjective and does not change form, singular or plural.

Avoid using a plural form for any of the adjectives joined by hyphens even when the noun that follows is plural.

Example :

they have a four-months-old baby.   ( incorrect)

they have a four-month-old baby.    (CORRECT)

a two-doors car is cheaper than a four-doors model.    (incorrect)

a two-door car is cheaper than a four-door model.        (CORRECT)