Bunuel wrote:

If each curved side in the figure above is a semicircle with radius 20, and the two parallel sides each have length 100, what is the area of the region by the above figure?

(A) 2,000

(B) 4,000

(C) 2000 – 200π

(D) 4,000 – 200π

(E) 4000 – 400 π

Attachment:

2017-11-16_1237.png

We will use a method called “cut and paste.” We see that we can cut the bottom semicircle out and paste it to the top so that the entire figure becomes a rectangle. The length of the rectangle will be 100 and the width will be the diameter or the semicircle, which is 40. Thus, the area of the rectangle, or the figure, is 100 x 40 = 4,000.

Answer: B

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