in a month/ for a month

Dear native English speakers,
Which would be used in the blank of each sentence, in or for?
1 I've been staying at this hotel ______ a month.
2 I haven't seen him ______ a month.
3 I'll begin to work ______ a month.
4 I worked for this company _____ a year.
5 It's only the second time I've been late _____ ten years.
6 Some of the books look as if they haven't been touched _____ years.

Thanks in advance.
Hirashin

1) for
2) for
3) in
=> note, "for" is ok if you mean the total duration of the work is a month.
4) for
5) in
6) both sound ok

Thanks for the help, mdchachi.