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Zargon Glasses

Age 7 to 11
Challenge Level

Why do this problem?

This problem is good for children who are confident with large numbers but need practice in finding combinations using a systematic method.

Key questions

What is the smallest number of lenses a family could need?
What is the greatest number of lenses a family could need?
How do you know you haven't got that combination already?

Possible extension

Children could investigate what would happen if some of the families have five eyes.

Possible support

It might be helpful for some children to use counters with either three or four dots on to represent the eyes.