Yes we can do them. We won't though, that's your job.

For a greatest common divisor, find the biggest number that you can divide both 1000 and 625 by. If you can't find the greatest common divisor, find any common divisor (there's a really obvious one), divide, then look for another common divisor. Keep doing this until you can't any more.

As for the lowest common multiple, write out the first few terms of the 1000 times table and the 625 times table. The lowest common multiple will be the first number that appears in both.