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18 Jun 2015, 02:53
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
25%
(medium)
Question Stats:
71% (01:18) correct
29%
(01:37)
wrong
based on 210
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.
(1) a = 3
(2) b – 3(5 – a ) = 0
Kudos for a correct solution.
18 Jun 2015, 03:08
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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
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
22 Jun 2015, 05:18
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Bunuel
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.
(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
The correct answer is B.
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!
