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## 'Sealed Solution' printed from http://nrich.maths.org/

A set of ten cards, each showing one of the digits from $0$ to $9$, is divided up between five envelopes so that there are two cards in each envelope. The sum of the two numbers inside it is written on each envelope:

What numbers could be inside the "8" envelope?

Thank you to Alan Parr for allowing us to adapt one of his problems.