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Question Stats:
47% (01:26) correct
52% (00:42) wrong based on 2 sessions
Is \frac{7^7}{7^x} an integer? 1. 0 \le x \le 72. |x|=x^2Source: GMAT Club Tests - hardest GMAT questions the indicated answer is B while I was sure it was D. I don't understand how 1 is not sufficient - IMHO it must be an integer. Thanks.
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Is 7^7 / 7^x an integer ? => Is 7^ (7-x) an integer ? The moment x is 7-x < 0 the equation does not result in an integer. Option A satisfies this condition. So A is sufficient. |x| = x^2 which means x = x^2 or -x=x^2 which implies x = 1 or x=-1 1 = 1^2 -(-1) = (-1)^2 So if x=1 7 ^ (7-1) is an integer if x=-1 7^(7-(-1)) is also an integer Hence option B is sufficient. The answer has to be D - are you sure it's B ? If so I might be missing something as well. -pradeep
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That's what it says:
Statement (1) by itself is insufficient. S1 says that can be between 0 and 7, so it can be an integer or any fraction.
Statement (1) by itself is sufficient. S2 implies that is one of (-1, 0, 1). .
The correct answer is B.
Anyway, it is probably just a bug. I wanted to make sure that I am not the only person who thinks that the indicated answer is wrong.
Thanks
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CIO
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Nowhere does S1 say that x is an INTEGER. If x is \frac{3}{2}, the expression from the question stem might look like this: \frac{7^7}{7^x} = \frac{7^7}{7^{\frac{3}{2}}} = \frac{7^7}{\sqrt{7^3}}Obviously, this is not an integer. Hope this helps. kotofei4 wrote: That's what it says:
Statement (1) by itself is insufficient. S1 says that can be between 0 and 7, so it can be an integer or any fraction.
Statement (1) by itself is sufficient. S2 implies that is one of (-1, 0, 1). .
The correct answer is B.
Anyway, it is probably just a bug. I wanted to make sure that I am not the only person who thinks that the indicated answer is wrong.
Thanks
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dzyubam wrote: Nowhere does S1 say that x is an INTEGER. If x is \frac{3}{2}, the expression from the question stem might look like this: \frac{7^7}{7^x} = \frac{7^7}{7^{\frac{3}{2}}} = \frac{7^7}{\sqrt{7^3}}Obviously, this is not an integer. Hope this helps. kotofei4 wrote: That's what it says:
Statement (1) by itself is insufficient. S1 says that can be between 0 and 7, so it can be an integer or any fraction.
Statement (1) by itself is sufficient. S2 implies that is one of (-1, 0, 1). .
The correct answer is B.
Anyway, it is probably just a bug. I wanted to make sure that I am not the only person who thinks that the indicated answer is wrong.
Thanks Dang !!!! I ALWAYS miss out on fractions ... Thanks so much dzyubam. +1
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This is a wonderfully written question and put in to your head - always check the question to make sure whether the value is integer /fraction
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Nice explanation..dzyubam...
I think whenever answering the questions relating to integers (number systems, in general), and where variables can assume a range of values, I try to imagine the diagram of a number line, with 0, +ve and -ve numbers...tht helps me tide over these questions.
Cheers,
R J
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we tend to assume any number as an integer..
but in GMAT, i have practiced many problems where i hv fell into this trap... beware....do not assume is one lesson i hv learnt...
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Statement 1 Insufficient because: When x = 2, The result is integer When x = 2.1, the result is non-integer Statement 2 is sufficient because: The only values that satisfy the given condition are: { -1, 0, 1}. All these 3 inputs for x give the Integer result. Hence, B Cheers! Ravi
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kotofei4 wrote: Is \frac{7^7}{7^x} an integer? 1. 0 \le x \le 72. |x|=x^2Source: GMAT Club Tests - hardest GMAT questions the indicated answer is B while I was sure it was D. I don't understand how 1 is not sufficient - IMHO it must be an integer. Thanks. we have \frac{7^7}{7^x} or 7^(7-x) lets start- stmt1- 0 \le x \le 7 -not suff, since we do not know whether x is integer or not. x could be 0 or 1/2 etc stmt 2- |x|=x^2 it means that x could be -1,0,1 . applying any of these numbers we get an integer. so, stmt 2 is suff
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Great question to highlight the trap that GMAT sets when working with integers and fractions. I too have fallen into it more than once and now always read the question carefully for words like "Integer", "Positive Integer" etc.
If none of these words are mentioned, I always assume that all numbers are valid. Here with the integer in the question, one can easily be thrown off assuming that x is also an integer, when clearly, it doesn't have to be.
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+1 for B too.
This question is a classic example of ZIP(Zero, Integer, Positive/Negative) trap.
BR
Mandy
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IMO B. S1 if x= 3 then answer is an integer if 3/2 then answer is not an integer. hence insufficient s2 x can be 1 0 or -1 hence sufficient
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B. Since in Statement 1 X can not be an integer so it cant be B. Statement 2 forces X to not only be an integer but to be equal to 0 or 1.
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For every data sufficiency question, Always apply the FOIN checks Can the variable in question assume any of the following types of values : Fraction 0Zero Integer or Irrational Negative
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In option 1, x need not be an integer.
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