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"Nothing is more interesting than nothing" — or so says Ian Stewart, Professor of Mathematics at Warwick University. Many people have difficulty with the concept of zero. In fact, it has only really been used as a number for the last 1500 years or so. Before this time it seems that zero was simply not that important. At the end of the day, a herd of no camels is not worth much.
Perhaps our ancestors were better off? Once you start using zero as a number then you can easily get into difficulty. Adding and taking away don't cause too much trouble, multiplication is straightforward (though a little unrewarding) but division simply has to be disallowed.
In a previous issue of PASS Maths we were asked what infinity multiplied by zero was. Our answer was that infinity cannot be multiplied by anything in the usual sense of the word because it is not a number. It's harder to explain away one divided by zero because they're both numbers; you're simply not allowed to do it.