In an electric circuit, two resistors with resistances x and

[email protected] wrote:Hi iMyself,

Visver's solution IS correct. This question can be found in the OG, so if you think that the provided solution is incorrect, then where did you find it?

GMAT assassins aren't born, they're made,
Rich

[email protected] wrote:HI iMyself,

This question appears in the OG13/GMAT2015/GMAT2016 on page 183 (although with slightly different question numbers). You can also feel free to read the explanation offered in any of those books. They all confirm the same answer.

GMAT assassins aren't born, they're made,
Rich

Brent@GMATPrepNow wrote:

iMyself wrote: So what? This is NOT your job to make comparison among those official guide edition (where is located this question); your job is to solve the question by seeing the question pattern!

Now that you've piqued our interest, what is the "correct" answer, and how is it derived?

iMyself wrote:In an electric circuit, two resistors with resistances x and y 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 reciprocal of the sum of x and y. What is r in terms of x and y ?

(A) xy
(B) x + y
(C)1/(x + y)
(D) xy/(x + y)
(E) (x + y)/xy

GMATGuruNY wrote:

iMyself wrote:In an electric circuit, two resistors with resistances x and y 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 reciprocal of the sum of x and y. What is r in terms of x and y ?

(A) xy
(B) x + y
(C)1/(x + y)
(D) xy/(x + y)
(E) (x + y)/xy

I received a PM requesting my input.

The reciprocal of r is equal to the reciprocal of the sum of x and y.
1/r = 1/(x+y).

Cross-multiplying, we get:
x+y = r.

The correct answer is B.

The problem posted above is an altered version of an official problem in the OG16.
The original problem -- which is trickier -- can be found here:
https://www.beatthegmat.com/reciprocals-t84790.html

[email protected] wrote:Hi All,

The original prompt actually differs from the one listed in the OGs (so it was either transcribed incorrectly or purposely changed).

In the OGs, the prompt states that "the reciprocal of R is equal to the SUM of the RECIPROCALS of X and Y."

In the post here, the prompt states that "the reciprocal of R is equal to the RECIPROCAL of the SUM of X and Y."

EVERYTHING else (including the 5 answer choices) is exactly the same though, so I'm led to believe that this question was mis-transcribed. With this transcription error, the "correct" answer would change though - it would become B.

GMAT assassins aren't born, they're made,
Rich

iMyself wrote:I've changed the question pattern intentionally..