I don't think you were adding properly. I get, for the perimeter of the un-fitted pieces,
and for the fitted pieces, I get
The difference is then or answer C.
Intermediate Mathematical Challenge 2010
Puzzle number 9
I'm not satisfied with the explanation because I did - to get
With the 26+4 pi being what I got from them being separate pieces
And the second part being the same way without using two 1s and four of 2pi over 2
Could anyone please help me?