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What is the value of 1/a + 1/b?

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What is the value of 1/a + 1/b?  [#permalink]

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New post 28 Feb 2016, 08:59
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A
B
C
D
E

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91% (00:51) correct 9% (00:58) wrong based on 96 sessions

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Re: What is the value of 1/a + 1/b?  [#permalink]

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New post 28 Feb 2016, 20:04
Bunuel wrote:
What is the value of 1/a + 1/b?

(1) a−b=10
(2) A+B=14


Hi Bunuel ,
It seems that statement 2 should be a+b = 14 . Otherwise , we would not be able to solve as we will have 2 equations and 4 variables .


(1) a−b=10
Not sufficient

(2) a+b = 14
Not sufficient

From 1 and 2 , we get
a=12
b=2
Now , we can calculate 1/a +1/b =1/12 + 1/2

Answer C
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Re: What is the value of 1/a + 1/b?  [#permalink]

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New post 29 Feb 2016, 00:49
Skywalker18 wrote:
Bunuel wrote:
What is the value of 1/a + 1/b?

(1) a−b=10
(2) A+B=14


Hi Bunuel ,
It seems that statement 2 should be a+b = 14 . Otherwise , we would not be able to solve as we will have 2 equations and 4 variables .


(1) a−b=10
Not sufficient

(2) a+b = 14
Not sufficient

From 1 and 2 , we get
a=12
b=2
Now , we can calculate 1/a +1/b =1/12 + 1/2

Answer C


Yes, it's a+b=14. Thank you.
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Re: What is the value of 1/a + 1/b?  [#permalink]

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New post 29 Feb 2016, 20:07
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

What is the value of 1/a + 1/b?

(1) a−b=10
(2) a+b=14


In the original condition, there are 2 variables(a,b), which should match with the number of equations. So you need 2 equations. For 1) 1 equation, for 2) 1 equation, which is likely to make C the answer.
When 1) & 2), they become a=12, b=2, which is unique and sufficient.
Thus, C is the answer.


 For cases where we need 2 more equations, such as original conditions with “2 variables”, or “3 variables and 1 equation”, or “4 variables and 2 equations”, we have 1 equation each in both 1) and 2). Therefore, there is 70% chance that C is the answer, while E has 25% chance. These two are the majority. In case of common mistake type 3,4, the answer may be from A, B or D but there is only 5% chance. Since C is most likely to be the answer using 1) and 2) separately according to DS definition (It saves us time). Obviously there may be cases where the answer is A, B, D or E.
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Re: What is the value of 1/a + 1/b?  [#permalink]

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Re: What is the value of 1/a + 1/b? &nbs [#permalink] 21 Mar 2017, 11:44
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