Any difference between "in" and "within"?

Is there any difference between the following two sentences?
- I'll finish the work in a couple of days
- I'll finish the work within a couple of days

Thank you.

>I'll finish the work in a couple of days

That suggests that the work will not be completed in anything less than a couple of days. At least a few days will pass before the work is completed.

>I'll finish the work within a couple of days

That suggests that the work might be completed sooner; the worst possible case is that it will take a couple of days to complete.

i agree with jacob. "...within a couple of days" means that it will be done either today, tomorrow, or (at the lastest) the day after tomorrow. "...in a couple of days" means you won't start it until the day after tomorrow.

wait... i misread your sentence. you said it will be finished in a couple of days. so i was wrong about it meaning that you won't start until the day after tomorrow. Jacob's explanation is right on.

What's the difference between these two sentences?

- I'll hand over my assignment by May 25.
- I'll hand over my assignment on May 25.

"I'll hand in my assignment by May 25th." (I could hand it in before May 25 or it could be on May 25...it has to be before or on May 25).

"I'll hand in my assignment on May 25th." (It will be handed in on the 25th of May...no sooner, no later).