In an electric circuit, two resistors with resistances 8 ohms and 9 ohms are connected in parallel. In this case, if R is the combined resistance of these two resistors, then the reciprocal of R is equal to the sum of the reciprocals of two resistors. What is R value ?
Select: A) 17 B) 45 / 78 C) 72 / 17 D) 17 / 72 E) 72

Rationale: the wording is a bit confusing , though basically we are told that 1 / r = 1 / 8 + 1 / 9 , from which it follows that r = 72 / 17 . answer : c .
Answer: C