Why do this problem?
This
activity offers practice in addition and subtraction, including
negative results, but the main aim is for pupils to concentrate on
making sure that all the ways of rolling the three dice are
reached. This will need some sort of system and you could focus on
how this could be recorded.
Possible approach
You could introduce the
problem using real dice and modelling the calculation a few times
so that pupils get a feel for it. Once a few results have been
recorded on the board, invite the pupils to speculate on how many
different results there might be.
Ask them to work in pairs
or small groups on the problem, saying very little else at this
stage, but after a short time, get them together again to share
insights so far. Discuss the range of answers that learners have
found up to that point and make sure they are happy with
subtracting one number from a smaller number. (Using a number line
which includes negative numbers might be helpful at this point.)
Invite some pairs to describe how they are working. Some may be
throwing real dice, others may be listing numbers. Encourage some
sort of system so that they can be sure no results are left out.
You could ask children to suggest ways of recording which would
help - this could be in the form of a table or chart, but allow
pupils to choose a way that suits them.
Key questions
What are all the
different possibilities that you found?
What are the final
answers by doing the addition and subtraction each time?
Is there a good way of
making sure you find all the possibilities?
How will you record what
you've found out?
Possible extension
Those children who are
beginning to use the probability scale from $0$ to $1$, could begin
to quantify the likelihood of getting particular results. Asking
and investigating 'What if ...?' questions would be another good
follow-up activity.
For the
highest-attaining
Pupils can be challenged
to use multiplication as well as addition and subtraction and then
after some experimentation try to predict totals that
will NOT be possible, then check these preditions out as well as
explaining the preditions.
Possible support
It can be helpful for
dice to be available, should children need them for reference. Some
pupils will benefit from an adult working alongside them and asking
questions along each step of the way until their confidence has
increased.