Weekly Problem 51 - 2010
The three angles of the triangle add to $180^{\circ}$, so the
combined area of the three sectors of the circles that are inside
the triangle add up to half a circle with area:
$\frac{1}{2} \times \pi \times \times 2^2 = \frac {4\pi}{2}=
2\pi$.
So the grey area is $(80- 2\pi) cm^2$.
