Maths+Problems

This problem is based on the 'Who can do the math?' game at Math Playground. We thank Colleen King for permission to modify this game and adapt it to our own classroom.

If each side of a pentagon measures 2 centimetres, what is the perimeter of Jake's pentagon chain?
Before you begin this challenge answer the following questions.

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This is what Kelly and her friend think.
"The first and last pentagons each have four sides that are part of the perimeter. The other 38 pentagons only contribute 3 sides each. That's 122 sides altogether. Since each side is 2 centimetres long the perimeter must be 244 centimetres." media type="custom" key="4597986"media type="custom" key="4503244"

This is what Astro and his friend think.
"A pentagon has 5 sides. Each side of a pentagon measures 2 centimetres. The perimeter of 1 pentagon is 10 centimetres. My design has 40 pentagons. I multiplied 40 by 10 to get the perimeter of the whole design. The perimeter is 400 centimetres." media type="custom" key="4503328" align="left"media type="custom" key="4503354" align="left"