Changed version of OG math...

[Black Hole]

Hi Instructor,
This question resembles Official Guide math, which official answer was "D". But I've slightly changed the question stem to confirm the answer option "B" is correct one. Is the question stem/version correctly being changed? or is there any flaw in this question stem?
Thanks...

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 reciprocals 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

[RonPurewal]

this question is fine, for reasons i discussed in detail here:
https://www.manhattanprep.com/gmat/foru ... ml#p118456

[RonPurewal]

it seems you've correctly understood the question.

your version just gives 1/r = 1/(x + y), which is ... well, not terribly interesting.
also, you would never see such a thing in a problem, because you would never see a real-world physics law written as "1/this = 1/that" when it could just as well be written as "this = that".
...but, yes, your understanding is correct.

in general, if you have the THIS of the THAT of this thing, then...
... you take 'this thing'
... you do THAT first
... you do THIS second (to the result of THAT)

[RonPurewal]

...although, actually, you did miss one thing.

this is going to seem like a tiny grammatical nuance—but, if you are having trouble deciphering the words, it can be a very easy 'key'.

you should have made this word SINGULAR:

the reciprocal of r is equal to the reciprocal of the sum of x and y

...because, in YOUR example, 1/(x + y) is only ONE 'reciprocal'.

in the original example, on the other hand, there are actually two reciprocals, namely 1/x and 1/y.

if you were having trouble deciding whether the correct expression was 1/(x + y) or 1/x + 1/y, you could have decided the issue with 100 per cent certainty simply by noticing that the letter 's' appears on the end of 'reciprocals'.
(:

[Black Hole]

Thank you.

[RonPurewal]

you're welcome.

[AsadA969]

Hey Ron,
I am little bit confused about this post. Here, in this creative question stem some words have been changed from the original OG question. It seems to look ok but this new question stem does not make any sense to me; it is just the combination of some facts, nothing else! The poster just makes some creativity in this question but it actually does not fulfill the mathematical demand at all. Here is my explanation about this question pattern. My explanation may be wrong. If I’m wrong then I’m sorry to bother you.

Here is my explanation:
Let, x=30 and y=40
From official guide: ‘……….sum of the reciprocals of x and y’.
Here, reciprocals of x and y is NOT like reciprocals of ‘x and y’. It is actually reciprocal of x and reciprocal of y, isn’t it? If yes then…..
So, reciprocal of x is 1/x (i.e., 1/30) and reciprocal of y is 1/y (i.e., 1/40). So, sum of the reciprocals of x and y is 1/x+1/y (i.e., 1/30+1/40)
In the new version, it is written as ‘reciprocal of the sum of x and y’. Here, it is actually NOT ….sum of ‘x and y’. It is just like ….sum of x and sum of y. So, we have to find out ‘the sum of x and the sum of y’ separately. So, the sum of 30 is what??----I don’t know. And the sum of 40 is what?---I also don’t know.
Ron, am I correct?
Thanks…

[RonPurewal]

i'm sorry, but i have no idea what you are trying to ask.