CK-12 Foundation
Ck 12: Geometry: Inscribed Similar Triangles
[Free Registration/Login may be required to access all resource tools.] Apply the fact that the altitude of a right triangle creates similar triangles.
University of Cambridge
University of Cambridge: Nrich: Elf Suits
Reasoning will help you figure out the various combinations of elf suits at this one page website. Check your solution against the solution given and see if they agree with you!