Sealed Solution

Ten cards are put into five envelopes so that there are two cards in each envelope. The sum of the numbers inside it is written on each envelope. What numbers could be inside the envelopes?
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative

Sealed Solution printable sheet

Here is a set of ten cards, each showing one of the digits from 0 to 9:

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Sealed Solution

The ten cards are 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:

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Sealed Solution

What numbers could be inside the "8" envelope?

Thank you to Alan Parr who inspired this task.