I was working in the library back then, and my sister was studying at college.

[Anna232]

I read on a website about punctuation that if both the independent clauses are short then some writers may choose to omit the comma before "and." But there is no example given. I will try to construct my own sentence.

"I was working in the library back then, and my sister was studying at college."
Is my understanding correct that the comma before "and" is optional?

 

[Rover_KE]

I consider it optional in that context, but I'm a comma minimalist and not every one will agree with me.