Funny Factorisation
Gabriel's Problem and Counting Factors might be good problems to try before looking at this one.
If you know the prime factors of a number, how can you work out which two-digit numbers are factors?
It might help to draw a factor tree.
If you'd like some help with the extension, click below
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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!
Double Digit
Choose two digits and arrange them to make two double-digit numbers. Now add your double-digit numbers. Now add your single digit numbers. Divide your double-digit answer by your single-digit answer. Try lots of examples. What happens? Can you explain it?
