I just read the Proof that all odd numbers are prime node and it reminded me of the following, something I picked up from a lecturer at University:

1. The Mathematician
"1 + 2 is 3 exactly."

2. The Physicist (for it is He)
i.  "1 + 2 is somewhere between 2.5 and 3.5."
ii. "Real physicists only deal in orders of magnitude. 1 + 2 is thus 1+ 1 which equals 1, as close as you need to worry about." (thanks to Albert Herring)

3. The Engineer
"1 + 2 is probably 3 but let's call it 10 to be on the safe side."

4. The Accountant
"1 + 2: how much do you want it to be?"