by Graham Smithers
Published: 7 August 2016 (link)
Beth wrote down a three-figure number and she also listed the five other three-figure numbers that could be made using those same three digits. Then she added up the six numbers: it gave a total whose digits were all different, and none of those digits appeared in her original number.
If you knew whether her original number was prime or not, and you knew whether the sum of the three digits of her original number was prime or not, then it would be possible to work out her number.
What was it?