"a day" and "per day"
When is it correct to say "a day" and when is it correct to say "per day" (pardon my prescriptive way of asking)? How interchangeable are they?
I have a rough idea but any rules governing this would be very useful.
I've already tried googling but the first result came up as "calories per day calculator".
Very grateful, IOU, etc.
I have a rough idea but any rules governing this would be very useful.
I've already tried googling but the first result came up as "calories per day calculator".
Very grateful, IOU, etc.