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 ?
Answers:
A) 17 B) 45/78 C) 72/17 D) 17/72 E) 72
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: 72/17.
<result>C</result>
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 ?