This talk about ANDs and ORs reminded me of one of my previous blood donations. One of the medical screening questions was, "In the past three years, have you been outside the US or Canada?"? I answered "Yes". The nurse asked me where I went and I told her that I had not left the US in the past three years. She asked why I answered "Yes". I said that it's an OR question. "...Have I been out of the US OR Canada?"? I'm outside of Canada right now. So I answered "Yes".? Logically, one cannot answer "No" to this question unless they have been straddling the border for the past three years.? I knew the intent of the question but, being a programmer, I answered it logically. Interestingly, there was a hand-out at the blood bank about foreign travel with the heading "Notice to people who traveled outside the US and Canada." The person who wrote the notice got the logic correct.? How many of us have gotten burned by misunderstanding the AND and OR logic?
Tom Hayes
Tom Hayes