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## 'I Like ...' printed from http://nrich.maths.org/

Mr Gilderdale was using this interactivity with his class:

This text is usually replaced by the Flash movie.

He had thought of a number rule and he asked the class to choose
numbers to test.

If the number they chose fitted his rule, he put it under 'I like
these numbers'. If the number they chose didn't fit his rule, he
put it under 'I don't like these numbers'.

Here is a picture of the game after the class had chosen four
numbers:

What could Mr Gilderdale's rule be?

If you were in Mr Gilderdale's class, which number would you choose
next to test your idea?

How could you find out Mr Gilderdale's rule in the smallest number
of guesses?