In an electric circuit, two resistors with 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 sum of reciprocals 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
The OA is D.
Please, can any expert explain this PS question for me? I don't understand why that is the correct answer. Thanks.
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In an electric circuit, two resistors with resistances x...
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Hi swerve,
We're told that the reciprocal of R is equal to the SUM of the reciprocals of X and Y. This question can be solved with TESTing Values.
Based on the wording of the prompt, we can create the following equation:
1/R = 1/X + 1/Y
We're asked for the value of R in terms of X and Y
If X = 2 and Y = 3, then we have...
1/R = 1/2 + 1/3
1/R = 3/6 + 2/6 = 5/6
R = 6/5
So we need an answer that = 6/5 when X = 2 and Y = 3. There's only one answer that matches...
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
We're told that the reciprocal of R is equal to the SUM of the reciprocals of X and Y. This question can be solved with TESTing Values.
Based on the wording of the prompt, we can create the following equation:
1/R = 1/X + 1/Y
We're asked for the value of R in terms of X and Y
If X = 2 and Y = 3, then we have...
1/R = 1/2 + 1/3
1/R = 3/6 + 2/6 = 5/6
R = 6/5
So we need an answer that = 6/5 when X = 2 and Y = 3. There's only one answer that matches...
Final Answer: D
GMAT assassins aren't born, they're made,
Rich
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- Master | Next Rank: 500 Posts
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- Joined: Wed Nov 29, 2017 4:38 pm
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in the statement itself he is telling reciprocal of r is equal to the sum of reciprocals of x and y which meansswerve wrote:In an electric circuit, two resistors with 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 sum of reciprocals 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
The OA is D.
Please, can any expert explain this PS question for me? I don't understand why that is the correct answer. Thanks.
1/r = 1/x + 1/y
or 1/r = (x+y)/xy
or r = xy/(x+y)
hence D the correct option.
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We are given that the reciprocal of r is equal to the sum of the reciprocals of x and y. Thus we can say:swerve wrote:In an electric circuit, two resistors with 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 sum of reciprocals 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
The OA is D.
Please, can any expert explain this PS question for me? I don't understand why that is the correct answer. Thanks.
1/r = 1/x + 1/y
Getting a common denominator for the right side of the equation, we have:
1/r = y / xy + x / xy
1/r = (y + x) / xy
If we reciprocate both sides of the equation, we have:
r = xy / (y+x)
Answer: D
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