If a - b = 5 and a2 + b2 = 34, find the value of ab.  Pick.
A) 4.5	B) 12	C) 15	D) 18	E) 20

Rationale: "explanation : 2 ab = ( a 2 + b 2 ) - ( a - b ) 2 = 34 - 25 = 9 ab = 4.5 . answer : a"
Answer: A