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# Prime Order

##### Age 11 to 14 ShortChallenge Level

Answer: None of them are prime

Numbers whose digits add up to a multiple of 3 are multiples of 3 (and numbers whose digits add up to a multiple of 9 are multiples of 9).
1 + 3 + 5 = 9, so any combination of the digits 1, 3, 5 will be a multiple of 3 (and 9).

This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.