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
Twenty. One to hold the bulb, two to turn the ladder, and seventeen on the guest list.
or
I guess that finally answers the question about how much Donald Trump is actually worth.
or
Five. Four to decide which way the bulb ought to turn, and . . .
or
Because he was feeling crumby.
or