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Diagonals
Age 14 to 16
ShortChallenge Level 
A square has 2 diagonals, a regular pentagon has 5 and a regular hexagon has 9.
How many diagonals does a regular icosagon (20 sides) have?
This problem is adapted from the South East Asian Mathematics Competition
You can find more short problems, arranged by curriculum topic, in our short problems collection.
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