Why do this
is a good context in which to encourage children
to work systematically to find all possibilities.
If $8$ is the first digit, what numbers are possible?
What could be the first digit instead of $8$?
How do you know you have all the possibilities?
If children are struggling to find a system, invite them to
write down different possible numbers on separate pieces of paper.
Once they have thought of as many as they can, work with them to
sort the numbers so that a pattern emerges and a structure is
imposed. In this way, learners will be able to spot any gaps for