1 Being students, they didn't have much money and they usually worked as waiters at weekends.
Why do we need to use the past simple?
2 While they were studying, they were working as waiters at weekends.
Is it right to use the past continuous in this case?
3 I worked from 09-00 to 18-00.
This means that I worked only from 09-00 to 18-00, right?
4 I was working from 09-00 to 18-00.
This means that I was in the process of working from 09-00 to 18-00, but I started work before 09-00 and is not a fact that I finished my work at 18-00. I am right?