Stage: 3 Challenge Level: 
If you were one of ten people at a party, how many times would you shake hands?
How many times would everyone else shake hands?
How could you use this to work out the total number of handshakes?
Check your method makes sense by trying some examples of small gatherings.
Visualising. Divisibility. Creating expressions/formulae. Triangle numbers. Generalising. Working systematically. Mathematical reasoning & proof. Interactivities. smartphone. Area.
Published October 2009.
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