Humpty Trumpty wants Mexico to pay for it all.
or
Nearly unanswerable, since the one who tries to change it usually drops it, and the others call for a planning session.
or
Answer: The back of his head.
or
To log on.
or
Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or