Why do 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.
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?
Learners could make their own number-crunching machine and try it out on their friends.
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.