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I'm sure you've heard about the response of Siri (Apple's "chat-bot") when asked what is 0 divided by 0. But can you divide by zero?  Isn't the problem that zero is not really a number, and if you treat it as though it is, you will get silly or weird results. So what is zero?  It's the numerical equivalent of nothing - it represents a lack of something.  In mathematics, a lack of quantity, a lack of value, a lack of number. And given that the division sum a/b asks the question "how many lots of b are there in a" this clearly only makes sense if b has a value.  If b is zero, then the question makes no sense.  Which is what Siri says, albeit in a humourous way.