grammar - Which is correct: "While studying, I ran my own business" or "While studying, I was running my own business"?

While studying, I ran my own business for almost two years.

This sounds natural to me, but my friend claims that the continuous form ("I was running") is gramatically correct. Which is it?

PS. In case it matters, this is in the context of a resume, so the idea is to sound formal.

Answer

Both are correct. The first sentence means that while doing the first action which is "studying" it was interrupted by the other action which is "running your own business" so you might no longer be doing the first action, but the second sentence means that you are doing both actions at the same time and none of them interrupted the other.