1) a ten years old boy is sitting on the couch.
2) a ten year old boy is sitting on the couch.
3) a ten-years old boy is sitting on the couch.
4) a ten-year old boy is sitting on the couch.
Which is correct?
Answer
Generally, when units of measure are used as adjectives, or as part of a compound noun, they are singular. When expressed as simple nouns, they are plural. Thus,
A ten-year-old boy is sitting on the couch.
The boy sitting on the couch is ten years old.
The boy sitting on the couch is a ten-year-old.
As for the hyphenation, exact usage is a matter of style, but the hyphen will determine how to interpret the phrase.
Ten year-old trees
refers to ten trees which are each one year old, whereas
Ten-year-old trees
refers to some trees which are each ten years old.
Attribution
Source : Link , Question Author : T2E , Answer Author : choster
