What is the sum of the angles at the blue vertices of this 11-gon?

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## Solution

The sum of angles is 900°.

Solution by Matthew Arcus: 11 turns, adding up to 6π, since we go round 3 times, each turn is π-α where α is the vertex angle, so 11π – ∑α = 6π, so ∑α = 5π = 900°.