Another Addition Edition

A patient requested a transfer of her controlled substance from another pharmacy. As I was about to pick up the phone, I noticed the label on the bottle from the other pharmacy said, "Must last 13 days", and it was last filled on the 14th. When this is written on a label, it's usually there by prescriber order. So, I called the patient over to inform her that I wouldn't be able to fill it until tomorrow and asked her if she still wanted me to transfer it. She responded, "Oh really? Why can't you fill it?" I said, "The doctor said it needs to last 13 days." She smartly replied, "Well that's funny, because I could swear on the paper I have a home that it says 14 days." Surely nobody is that stupid, but I took advantage by saying, "Really? That means I can't fill it until the 28th then." As I was being entertained by the puzzled look on her face, she quickly said, "I mean, 13 days, but it's the 13th day today, right?" Actually, no. I did one of my classic "this plus this equals that" comments, and said, "You filled it on the 14th, and 14 plus 13 is 27." She took her bottle back and asserted that she'd just go back to where she got it filled last, because certainly they would fill it for her. That's only if they have similar trouble with addition.