This Cross-Number puzzle involves the use of a novel 'reverse notation' or 'looking glass arithmetic'. Students should be encouraged to investigate and discover rules for adding and subtracting digimirror numbers.
A detailed teacher's guide is included which suggests possible classroom approaches. Answers are provided.
My resource 'Digimirror Maths' would be a natural introduction to this activity.
[Number bases, decimal system, place value, number puzzle, reflection, addition & subtraction of integers]