Some question: Consider a quarter of a circle of radius 20. Let r be the radius of the circle inscribed in this quarter of a circle. Find r.
Options:
(A) 20*(sqr2 -1) 
(B) 8*(sqr3 -1) 
(C) 4*(sqr7 - 1) 
(D) 12* (sqr7 -1) 
(E) None of these
Some stream of consciousness:
I got 20/(sqr2 +1) and just forgot to multiply by (sqr2 -1). The answer: (A).