Lemonade.
or
Fifty — one to screw in the bulb and 49 to guard him/her.
or
To get to the baaaaarber shop
or
Two. One to screw it in, and one to stab the other in the back and take all the credit.
or
proving once and for all that you can't have your kayak and heat it.
or
Five. Four to decide which way the bulb ought to turn, and . . .
or