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Adding All Nine

Make a set of numbers that use all the digits from 1 to 9, once and once only. Add them up. The result is divisible by 9. Add each of the digits in the new number. What is their sum? Now try some other possibilities for yourself!

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Have You Got It?

Can you explain the strategy for winning this game with any target?

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Counting Factors

Is there an efficient way to work out how many factors a large number has?

American Billions

Age 11 to 14 Challenge Level:

You may find an article on Divisibility Tests helpful.

Have a go at the interactive problem Dozens first, to practise applying your understanding of the divisibility rules.