Which is correct in each example One half piece of pie One-half piece of pie I gave her one half I gave her one-half follow up appointment follow-up appointment?

The correct forms are "one-half piece of pie," "I gave her one-half," and "follow-up appointment." In these examples, "one-half" is used as a compound adjective or a noun modifier, and "follow-up" is a compound adjective describing the type of appointment. Using hyphens in these cases clarifies the relationships between the Words.