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The mean is a type of average of a set of numbers.
The mean is the total of the numbers divided by how many numbers there are. 
 

Try starting with a specific example.

e.g.
Group A is composed of people aged 2, 7, 11, 14 and 16 (average 10)
Group B is composed of people aged 5, 11, 12, 13 and 19 (average 12)

Investigate what happens to the averages when different members move from one group to the other.

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The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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