Method is based on the above given paper.
Could be, I am quoting source as it was listed in the book from which I took the problem.
Calibration curve makes the measurement easier and faster, and takes some unpredictable factors into account. Problem was about theoretical approach and calculations are based on several assumptions (no heat loses, 100% conversion of CO to CO2
What I like about the problem is that it is about clever use of basic physics/chemistry for practical purposes. You can teach students about heat balance for months, but they don't know what for they learn it. Show them this question, explain how dangerous CO is, and chances are they will see it all makes sense.