Three. One to change it while the other two argue about how old the old one is.
Is the lightbulb plugged in sir?
Just one, but it takes a really long time, and the lightbulb has to want to change...
100. 1 to change the light bulb and the other 99 to complain about how the old light bulb was much better.
1 or 2? 1... or 2?
Because of his enthusiasm for Carbon-Dating.
Because they cant find dates
5. 1 to screw in the light bulb, and 4 to remark on how grand the old one was.