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Sisters and Brothers
Age 7 to 11
Challenge Level 
Why do this problem?
This problem encourages children to use number operations and
either trial and improvement, or a systematic approach to reach a
solution. It would be interesting to share the different ways they
use jottings to help during the problem-solving
process. The problem could be used to introduce
algebraic notation.
Key questions
What could you try to start with?
What does that tell you about the ages of the other
children?
What do you know about David's age compared with Lachlan's
age?
Possible extension
Learners could make up another similar problem for a friend to
solve.
Possible support
You could ask questions such as 'what if Lachlan is one year
old?' and encourage children to work out the ages of Cassandra and
David to see whether all the information holds true. If not, invite
learners to suggest what to try next.
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