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The Number Crunching Machine
Age 7 to 11
Challenge Level 
The Number Crunching Machine
Put a number at the top of the machine and collect a number at the bottom.
What do you get?
Which numbers get back to themselves?
Why do this problem?
This problem is an amusing and thought-provoking way of practising addition, subtraction, multiplication and division. The results are diverse enough to keep learners working for a considerable time and to encourage methodical working. This sheet might be helpful.
Key questions
What operation do you need to do next?
Would it be a good idea to jot down your calculations as you go?
What numbers have you put in so far?
Have you made a list of the numbers you have already done?
How many numbers have you found that come out unchanged?
Possible extension
Learners could make their own number-crunching machine and try it out on their friends.
Possible support
Suggest trying with different numbers below $50$. It may help to make a version going across the page with arrows or you could use this sheet.You may also like
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