Why do this
problem?
This problem would make a good starter for those children who
are working on the writing and ordering the numbers from $1$ to
$20$, and might be suitable for use in conjunction with a number
line.
Possible approach
You could display a number line and ask the group to count
outloud along it with you. You could then show them a number line
just numbered up to $5$, as in the picture. Encourage the children
to count along this number line, filling in the blanks as they
go.
Then, introduce the problem orally and ask learners to work in
pairs on the challenge, with their own number line to help. It may
be necessary to clarify the meaning of 'digit' if the children are
not familiar with this term.
Key questions
What do we mean by 'digit'?
Which is the tenth digit? How do you know?
Possible extension
Pose similar questions for the children, such as "If Lee wrote all
the numbers from $1$ to $20$, how many digits would she have
written altogether?" "How many sevens has Lee written? What digit
did she write after each of these sevens?"
Possible support
Children could be encouraged to count carefully along a number
line.