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 not be doing the first action but the second sentence means that you are actually doing both steps at the same time.

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 not be doing the first action but the second sentence means that you are actually doing both steps at the same time.