As an engineer, I love stories that discomfit mathematicians (many of whom regard engineers as a species of lower pond-life). So this one from the late Neil Armstrong cheered me up no end.

“Two students, a young man and a young woman, are standing 10m apart. Every 15 seconds, the young man halves the distance between him and the young woman – so how long will it take for them to get together?” The mathematician in the class immediately answers ‘Never – it’s an infinite series and they never actually meet’. The engineer in the class thinks for a moment and then comes up with a different answer: ‘Two and a half minutes’. Why? ‘Because after two-and-a-half minutes, they will be close enough for all practical purposes!'”

Thanks to Ian Yorston for spotting it.