Khan/khan-exercises — pull request #25555 by osnr (2012-07-06 22:53:49+00:00)
Title: Add area exercises

Exercises here:
* Circles and arcs
* Shaded areas
* Areas of circles and sectors
* Area of parallelograms
* Areas of trapezoids, rhombi, and kites

Remaining for me to do:
* Regular polygons
* Perimeters and areas of similar figures
* Trigonometry and area [hard regular polygons]

(How do I get a sandcastle?)