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Updated on: 20 Apr 2015, 04:35
Originally posted by mpcostello on 19 Apr 2015, 11:32.
Last edited by Bunuel on 20 Apr 2015, 04:35, edited 2 times in total.
Last edited by Bunuel on 20 Apr 2015, 04:35, edited 2 times in total.
Renamed the topic, edited the question, added the OA and moved to DS forum.
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D
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Difficulty:
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Question Stats:
82% (00:56) correct
18%
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wrong
based on 220
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If x and y are integers, is xy even?
(1) x = y + 1.
(2) x/y is an even integer.
OPEN DISCUSSION OF THIS QUESTION IS HERE: if-x-and-y-are-integers-is-xy-even-137508.html
(1) x = y + 1.
(2) x/y is an even integer.
Correct answer is D. I understand the explanation for 1) that the formula suggests that x and y are consecutive integers in which case on is even and one is off and odd x even is even.
BUT...I divided x by y ie x/y = 1. This indicates that x=y as 1/1 = 1 and 3/3 = 1 as there is no knowing if the numbers or odd or even I had this point 1 a NS. This is wrong but was hoping someone could explain why my own method/thinking is inaccurate.
Thanks!
BUT...I divided x by y ie x/y = 1. This indicates that x=y as 1/1 = 1 and 3/3 = 1 as there is no knowing if the numbers or odd or even I had this point 1 a NS. This is wrong but was hoping someone could explain why my own method/thinking is inaccurate.
Thanks!
OPEN DISCUSSION OF THIS QUESTION IS HERE: if-x-and-y-are-integers-is-xy-even-137508.html
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19 Apr 2015, 19:00
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Hi mpcostello,
The prompt tells us that X and Y are integers. Fact 2 tells us that X/Y is an EVEN INTEGER.
Neither of your examples fits the 'restriction' described by Fact 2.
1/1 = 1 which is NOT an EVEN integer
3/3 = 1 which is NOT an EVEN integer
Thus, you haven't proven anything yet. TESTing VALUES is a great way to prove what's going on in Fact 2, but you have to use values that fit what you're told.
GMAT assassins aren't born, they're made,
Rich
The prompt tells us that X and Y are integers. Fact 2 tells us that X/Y is an EVEN INTEGER.
Neither of your examples fits the 'restriction' described by Fact 2.
1/1 = 1 which is NOT an EVEN integer
3/3 = 1 which is NOT an EVEN integer
Thus, you haven't proven anything yet. TESTing VALUES is a great way to prove what's going on in Fact 2, but you have to use values that fit what you're told.
GMAT assassins aren't born, they're made,
Rich
19 Apr 2015, 22:55
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mpcostello
Dear Mpcostello
You were right in trying different values of x and y because as you said, at this point, we had no way of knowing whether x and y are odd or even. However, the point where you went wrong was that you considered such values of x and y that violated the information given in St. 2. Statement 2 clearly mentioned that x/y is an Even integer. However, both the sets of (x,y) values that you considered led to an odd value of x/y (1).
Actually, in this case, instead of going down the 'plugging different values of x and y' route, processing Statement 2 from the first principles would have been easier and would also have taken lesser time. Here's how I would have thought through this Statement:
x/y = Even Integer
=> x = (y)*(Even Integer)
=> x is an Even integer
=> Product xy = (Even integer x)*(y)
=> Product xy will definitely be Even.
Therefore, Statement 2 is sufficient.
So, the takeaway I hope you learn from your mistake in this question is:
- When taking the 'plugging in numbers' approach, be very careful that the chosen numbers do not violate the constraints given in the question.
Hope this helped.
- Japinder
D) 
