1. I want six slices of
apples. From more than one apple (OK)
2. I want six slices of
apple. From one apple (OK)
3. I'll have ten dollars worth of gas. (OK) non-count
4. I'll have ten dollars worth of
apples. (OK) count
5. I'll have ten dollars worth of
apple. (OK) Iff 'apple' is modifying a non-count noun e.g., apple (sauce), apple (candy), apple (gas)