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Re: If x is a positive number [#permalink]
26 Aug 2012, 05:42
2
This post received KUDOS
Expert's post
2
This post was BOOKMARKED
If x is a positive number, is x an even integer?
Notice that we are not told that x is an integer.
(1) 3x is an even integer. x could be ANY even number or some fraction (for example 2/3), so this statement is NOT sufficient.
(2) 5x is an even integer. The same here, x could be ANY even number or some fraction (for example 2/5). Not sufficient.
(1)+(2) We have that 3x=even and 5x=even. Subtract one from another: 5x-3x=even-even --> 2x=even --> x=even/2=integer. Now, x=integer and 3x=even (from 1) means that x must be an even integer. Sufficient.
Re: If x is a positive number [#permalink]
26 Aug 2012, 08:13
syog wrote:
If x is a positive number, is x an even integer?
(1) 3x is an even integer.
(2) 5x is an even integer.
Neither (1) nor (2) alone is sufficient.
(1) and (2) together:
From (1) \(3x=2k,\) where \(k\) is a positive integer. From (2) \(5x=2m,\) where \(m\) is some positive integer. Necessarily \(\frac{2k}{3}=\frac{2m}{5}\) from which \(5k=3m.\) \(k\) and \(m\) being integers, necessarily \(k\) must be a multiple of 3 (because 5 is not divisible by 3), so \(k=3a\) for some positive integer \(a.\) It follows that \(x=\frac{2k}{3}=2a\) so \(x\) is even.
Sufficient.
Answer C _________________
PhD in Applied Mathematics Love GMAT Quant questions and running.
Re: If x is a positive number [#permalink]
30 Aug 2012, 03:53
Bunuel wrote:
If x is a positive number, is x an even integer?
Notice that we are not told that x is an integer.
(1) 3x is an even integer. x could be ANY even number or some fraction (for example 2/3), so this statement is NOT sufficient.
(2) 5x is an even integer. The same here, x could be ANY even number or some fraction (for example 2/5). Not sufficient.
(1)+(2) We have that 3x=even and 5x=even. Subtract one from another: 5x-3x=even-even --> 2x=even --> x=even/2=integer. Now, x=integer and 3x=even (from 1) means that x must be an even integer. Sufficient.
Answer: C.
My answer to this question was D, both sufficient, however my assumption was that in GMAT number and integer are interchangible words, but as i see i was wrong. Bunuel could you please remind what word was interchangible with word integer? _________________
If you found my post useful and/or interesting - you are welcome to give kudos!
Re: If x is a positive number [#permalink]
30 Aug 2012, 04:18
Expert's post
1
This post was BOOKMARKED
ziko wrote:
Bunuel wrote:
If x is a positive number, is x an even integer?
Notice that we are not told that x is an integer.
(1) 3x is an even integer. x could be ANY even number or some fraction (for example 2/3), so this statement is NOT sufficient.
(2) 5x is an even integer. The same here, x could be ANY even number or some fraction (for example 2/5). Not sufficient.
(1)+(2) We have that 3x=even and 5x=even. Subtract one from another: 5x-3x=even-even --> 2x=even --> x=even/2=integer. Now, x=integer and 3x=even (from 1) means that x must be an even integer. Sufficient.
Answer: C.
My answer to this question was D, both sufficient, however my assumption was that in GMAT number and integer are interchangible words, but as i see i was wrong. Bunuel could you please remind what word was interchangible with word integer?
I think you refer to Natural Numbers, which are non-negative (or positive) integers but GMAT doesn't use words "Natural Number" in their questions.
So, there is no interchangeable word for "integer" on the GMAT. _________________
Re: If x is a positive number [#permalink]
02 Sep 2013, 07:23
Bunuel wrote:
ziko wrote:
Bunuel wrote:
If x is a positive number, is x an even integer?
Notice that we are not told that x is an integer.
(1) 3x is an even integer. x could be ANY even number or some fraction (for example 2/3), so this statement is NOT sufficient.
(2) 5x is an even integer. The same here, x could be ANY even number or some fraction (for example 2/5). Not sufficient.
(1)+(2) We have that 3x=even and 5x=even. Subtract one from another: 5x-3x=even-even --> 2x=even --> x=even/2=integer. Now, x=integer and 3x=even (from 1) means that x must be an even integer. Sufficient.
Answer: C.
My answer to this question was D, both sufficient, however my assumption was that in GMAT number and integer are interchangible words, but as i see i was wrong. Bunuel could you please remind what word was interchangible with word integer?
I think you refer to Natural Numbers, which are non-negative (or positive) integers but GMAT doesn't use words "Natural Number" in their questions.
So, there is no interchangeable word for "integer" on the GMAT.
I am a little confused. 1) 3x is an even integer. Let x=4/3; then 3x=4. But in this case x is not an even integer. Hence INSUFFICIENT.
2) 5x is an even integer. Let x=4/5; then 5x=4. But in this case x is not an even integer. Hence INSUFFICIENT.
(1+2): 15x is an integer. Let x=4/15; then 15x=4. But in this case x is not an even integer. Hence INSUFFICIENT.
Re: If x is a positive number [#permalink]
02 Sep 2013, 07:42
Expert's post
domfrancondumas wrote:
Bunuel wrote:
ziko wrote:
If x is a positive number, is x an even integer?
Notice that we are not told that x is an integer.
(1) 3x is an even integer. x could be ANY even number or some fraction (for example 2/3), so this statement is NOT sufficient.
(2) 5x is an even integer. The same here, x could be ANY even number or some fraction (for example 2/5). Not sufficient.
(1)+(2) We have that 3x=even and 5x=even. Subtract one from another: 5x-3x=even-even --> 2x=even --> x=even/2=integer. Now, x=integer and 3x=even (from 1) means that x must be an even integer. Sufficient.
Answer: C.
My answer to this question was D, both sufficient, however my assumption was that in GMAT number and integer are interchangible words, but as i see i was wrong. Bunuel could you please remind what word was interchangible with word integer?
I think you refer to Natural Numbers, which are non-negative (or positive) integers but GMAT doesn't use words "Natural Number" in their questions.
So, there is no interchangeable word for "integer" on the GMAT.
I am a little confused. 1) 3x is an even integer. Let x=4/3; then 3x=4. But in this case x is not an even integer. Hence INSUFFICIENT.
2) 5x is an even integer. Let x=4/5; then 5x=4. But in this case x is not an even integer. Hence INSUFFICIENT.
(1+2): 15x is an integer. Let x=4/15; then 15x=4. But in this case x is not an even integer. Hence INSUFFICIENT.
Notice that x cannot be 4/15, because in this case 3x=12/15 which is NO an even integer and 5x=20/15 which is also NOT an even integer, so in this case both statements are violated. _________________
Re: If x is a positive number [#permalink]
10 Oct 2014, 09:16
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