For example, to answer the question, "How tall are you?" valid answers include:
- Five feet.
- Five foot three.
- Five feet, three inches.
Why the discrepancy between feet and foot, seemingly only in the second case.
This question is inspired by this question: "Forty foot" or "forty feet"?
edit: I do not believe the answer to this is related to the other question. The explanation for the other question is because of how adjective modifiers work. My question is a very different case, unrelated to adjectives. My observation is that I am asking about a particular exception case which applies only when "foot" is followed by a number which is assumed to be inches. That's extremely specific, and I doubt that the etymology has any relation to why we leave adjective modifiers singular.