Why do this
At the very simplest level
is an investigation involving estimation and trial and
improvement. The greater depth comes from realising that changing
any one corner number affects two others and that this means
keeping two conditions in mind simultaneously.
What would be good 'rough' numbers to start with?
When you make this one smaller what happens?
Children can make up their own for others to solve. They could
explore the differences between using odd/even numbers in the
Making up questions like these can be a form of support. Start
with smaller numbers so that the arithmetic does not get in the way
of the thinking.