I posted this joke I came up with myself years ago on my Dutch blog and now tried to translate and update it:

• Answer 1: none, the light bulb has to discover itself how to get into the fitting.
• Answer 2: why use light bulbs when there are candles?
• Answer 3: still using light bulbs? Why don’t you try an iPad? Or the block chain?
• Answer 4: 1 teacher trainer and 15 teacher trainees who will take turns to change the light bulb again and again while the others take notes on 2 strong points and 2 points that need working on.