Someone asked me about this today, so I thought I’d pass it on:
When you are writing numbers, generally one thru ten are spelled out. The rest aren’t. So we spell “seven”, but not 17.
I break this rule often, though (it’s not really a rule, but more of a handshake agreement.) Why do I break it? Because “we handle any size job, from 3 pages to 300” catches the eye better than “we handle any size job, from three pages to 300” (although the second one actually looks more professional when reading – so it’s really about what you are after – scan-ability, or a professional read.)
Anyway, just thought I’d share that.