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Is a^b>0?

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Is a^b>0?  [#permalink]

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New post 08 Dec 2017, 01:06
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A
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C
D
E

Difficulty:

  5% (low)

Question Stats:

82% (00:29) correct 18% (00:20) wrong based on 68 sessions

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[GMAT math practice question]

Is \(a^b>0\)?

1) \(a\) is positive
2) \(b\) is a prime number

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Re: Is a^b>0?  [#permalink]

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New post 08 Dec 2017, 01:31
MathRevolution wrote:
[GMAT math practice question]

Is \(x= a^b>0\)?

1) \(a\) is positive
2) \(b\) is a prime number



Pl correct the Question..
Most likely it should be is a^b>0..

1) a is positive..
Whatever be the value of b, a^b>0
Suff

2) b is a prime number..
If it is 2, Ans will be YES always..
Otherwise it will depend on a.
Insufficient

A
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Re: Is a^b>0?  [#permalink]

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New post 08 Dec 2017, 02:21
(1) a is positive, hence any value of b wqould give us positvie result
Sufficient
(2) b can take 2;3;7 etc
a= -1 ; b=2 then x would be +ve
a=-1 ; b=3 then x would be -ve
Insufficient

Answer A.
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Re: Is a^b>0?  [#permalink]

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New post 10 Dec 2017, 18:12
=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA method is to modify the original condition and the question, and then recheck the question.

Condition 1)
If \(a > 0\), then \(a^b>0\). The answer is ‘yes’.
So, this condition is sufficient.

Condition 2)
For \(a = 2, b = 2\), we have \(a^b = 2^2 = 4 > 0\), and the answer is ‘no’.
For \(a = -2, b = 3\), we have \(a^b = (-2)^2 = -8 < 0\), and the answer is ‘yes’.
So, condition 2) is not sufficient.
Therefore, the answer is A.

Normally, in problems which require 2 or more additional equations, such as those in which the original conditions include 2 variables, or 3 variables and 1 equation, or 4 variables and 2 equations, each of conditions 1) and 2) provide an additional equation. In these problems, the two key possibilities are that C is the answer (with probability 70%), and E is the answer (with probability 25%). Thus, there is only a 5% chance that A, B or D is the answer. This occurs in common mistake types 3 and 4. Since C (both conditions together are sufficient) is the most likely answer, we save time by first checking whether conditions 1) and 2) are sufficient, when taken together. Obviously, there may be cases in which the answer is A, B, D or E, but if conditions 1) and 2) are NOT sufficient when taken together, the answer must be E).

Answer: A
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Re: Is a^b>0?  [#permalink]

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New post 08 Jul 2018, 03:02
1
MathRevolution wrote:
[GMAT math practice question]

Is \(x= a^b>0\)?

1) \(a\) is positive
2) \(b\) is a prime number



Can moderator please correct the question, x should not be in the question. Thank you.
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Re: Is a^b>0?  [#permalink]

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New post 08 Jul 2018, 03:43
stne wrote:
MathRevolution wrote:
[GMAT math practice question]

Is \(x= a^b>0\)?

1) \(a\) is positive
2) \(b\) is a prime number



Can moderator please correct the question, x should not be in the question. Thank you.

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Done. Thank you.
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Re: Is a^b>0? &nbs [#permalink] 08 Jul 2018, 03:43
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