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Pentagon Ring

Stage: 3 Short Challenge Level: Challenge Level:3 Challenge Level:3 Challenge Level:3
See all short problems arranged by curriculum topic in the short problems collection

Equal regular pentagons are placed together to form a ring.  
The diagram shows the first three pentagons.

How many pentagons are needed to complete the ring?

circle with chain of 3 pentagons.

 

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

This problem is taken from the UKMT Mathematical Challenges.