72 // If You Thought Mathematicians were Good at Arithmetic . . .

If You Thought Mathematicians were Good at Arithmetic . . . Ernst Kummer was a German algebraist, who did some of the best work on Fermat's Last Theorem before the modern era. However, he was poor at arithmetic, so he always asked his students to do the calculations for him. On one occasion he needed to work out 967. `Umm . . . nine times seven is . . . nine times . . . seven . . . is . . . '

`Sixty-one,' suggested one student. Kummer wrote this on the blackboard.

`No, Professor! It should be sixty-seven!' said another.

`Come, come, gentlemen,' said Kummer. `It can't be both. It

........................................... must be one or the other.'

The Sphinx is a Reptile Well, a rep-tile, which isn't quite the same thing. Short for `replicating tile', this word refers to a shape that appears ­ magnified ­ when several copies of it are put together. The most obvious rep-tile is a square.

Four square tiles make

a bigger square.

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