Question

1. He walked for ten miles.
2. He walked ten miles.
[Are both grammatical?]

3. He slept for seven hours.
4. He slept seven hours.
[Are both grammatical?]

5. I have lived here for five years.
6. I have lived here five years.
[What about this pair? can we use #6? Can we delete 'for' as in #6?]

Answer 1

Yes, all are fine. You can use these with or without “for.”