4,000
If you mean 5000/1000, then the answer is 5/1, which is 5.
50 x 100 etc etc...
Sounds like a good trick. You're not going to get 5000 l of water in a 1000 l container. It is like carrying around a 2 l bottle with 10 l of soda in it. Unless you're from Gallifrey, it is not going...
The pattern is to divide by 5, so the next number would be 40