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Cereal Packets

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Sealed Solution

Stage: 2 Challenge Level: Challenge Level:2 Challenge Level:2

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:

five envelopes with the numbers 7, 8, 13, 14 and 3 written on them (one number per envelope)

What numbers could be inside the "8" envelope?

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


The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice. More information on many of our other activities can be found here.
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NRICH is part of the family of activities in the Millennium Mathematics Project.