R.J. Valentine:
> Also someone might be working at getting promoted
Yes.
> while working on completing the project on time.
No, I think that's better with "at". They're working on the project
and working at completing it on time.
You "work on" a specific task; you "work at" a goal.
However, if the task is a big one that you don't think you can complete
in a reasonable time, then you might view it more like a goal and speak
of "working at" it. For example, "I worked at cleaning up the mess for
a while, but you can hardly tell I did anything."
Someone else referred to working at a company. That's the ordinary
verb "work" followed by a phrase that happens to begin with "at"; it's
not the phrasal verb "work at".

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Mark Brader | But I think we can do better next time. (Where the
Toronto | word "we" refers to [those] who do the hard work while
msb@vex.net | I sit back and complain...) -- Keith Thompson
My text in this article is in the public domain.