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#### Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.  # If K = (1/(3a) + 1/b)/(5/(ab)) and ab ≠ 0, what is the value of K ?

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Math Expert V
Joined: 02 Sep 2009
Posts: 59589
If K = (1/(3a) + 1/b)/(5/(ab)) and ab ≠ 0, what is the value of K ?  [#permalink]

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1 00:00

Difficulty:   35% (medium)

Question Stats: 69% (01:18) correct 31% (01:38) wrong based on 115 sessions

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If $$K = \frac{\frac{1}{3a} + \frac{1}{b}}{\frac{5}{ab}}$$ and ab ≠ 0, what is the value of K ?

(1) a = 3
(2) b – 3(5 – a ) = 0

Kudos for a correct solution.

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Board of Directors D
Joined: 01 Sep 2010
Posts: 3417
Re: If K = (1/(3a) + 1/b)/(5/(ab)) and ab ≠ 0, what is the value of K ?  [#permalink]

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1
Simplified we do have 3a+b/15 so we need these values

A) insufficient we have only the value of a but not b

B) sufficient. we do have directly the value of 3a= -b + 15. The we do have 15/15=1

B wins
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Math Expert V
Joined: 02 Sep 2009
Posts: 59589
Re: If K = (1/(3a) + 1/b)/(5/(ab)) and ab ≠ 0, what is the value of K ?  [#permalink]

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Bunuel wrote:
If $$K = \frac{\frac{1}{3a} + \frac{1}{b}}{\frac{5}{ab}}$$ and ab ≠ 0, what is the value of K ?

(1) a = 3
(2) b – 3(5 – a ) = 0

Kudos for a correct solution.

MANHATTAN GMAT OFFICIAL SOLUTION:

It should be evident that the two statements combined are sufficient to answer the question—you can plug the value of a from Statement (1) into Statement (2) to solve for the value of b, then you can plug those values into the question to solve for K.

Immediately be skeptical. C should seem too easy. After all, you didn't do anything to the question stem. So you should do some work to determine whether one of the two statements alone (or, in some cases, each statement alone) is sufficient to answer the question.

Let's start by rephrasing the question:

$$K = \frac{\frac{1}{3a} + \frac{1}{b}}{\frac{5}{ab}}=\frac{\frac{b}{3ab} + \frac{3a}{3ab}}{\frac{5}{ab}}=\frac{b+3a}{3ab}*\frac{ab}{5}=\frac{b+3a}{15}$$

“What is the value of K?” rephrases to “What is the value of b + 3a?” Statement (2) rephrases and gives us the answer:
b – 3(5 – a) =
b – 15 + 3a = 0
b + 3a = 15

This is not a tactic to use at lower levels of the test. On 500-600 level problems, the two statements may work together in straightforward ways to produce sufficiency. The C trap may be the C answer!
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GMAT 1: 650 Q43 V37 GRE 1: Q157 V158 GPA: 2.66
Re: If K = (1/(3a) + 1/b)/(5/(ab)) and ab ≠ 0, what is the value of K ?  [#permalink]

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Bunuel wrote:
If $$K = \frac{\frac{1}{3a} + \frac{1}{b}}{\frac{5}{ab}}$$ and ab ≠ 0, what is the value of K ?

(1) a = 3
(2) b – 3(5 – a ) = 0

Kudos for a correct solution.

Always try to rewrite the original equation in ds suff to find the true question

St 1

Still cannot solve for b +3a

St 2

Distribute (though this was a foiling question at first).

b- 15+3a= -
b+3a= 15

suff

B
Attachments image1.JPG [ 662.54 KiB | Viewed 537 times ] Re: If K = (1/(3a) + 1/b)/(5/(ab)) and ab ≠ 0, what is the value of K ?   [#permalink] 10 Sep 2017, 13:31
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# If K = (1/(3a) + 1/b)/(5/(ab)) and ab ≠ 0, what is the value of K ?  