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by GmatKiss » Sun Oct 16, 2011 9:25 am
achieve_dream wrote:If X AND Y are integers, is x-1 >= y?

1) x is a positive multiple of y
2) (x/y) >1

Official Answer C

My answer was B.
Can you please explain the official answer?
Please post answer with spoiler.
It makes no sense for those (including me) who look out to solve a problem in the forum.
Last edited by GmatKiss on Sun Oct 16, 2011 10:08 am, edited 1 time in total.
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by achieve_dream » Sun Oct 16, 2011 9:41 am
I don't think knowing the answer should impact the way one solves the question. However, I just put a spoiler around it.
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by GmatKiss » Sun Oct 16, 2011 10:08 am
achieve_dream wrote:I don't think knowing the answer should impact the way one solves the question. However, I just put a spoiler around it.
Psychologically, it does drag us to look out for stuffs favouring the answer!
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by leonswati » Sun Oct 16, 2011 10:36 am
achieve_dream wrote:If X AND Y are integers, is x-1 >= y?

1) x is a positive multiple of y
2) (x/y) >1

Official Answer C


Statement 1:
X = n*Y ; n is an integer greater than 0

Let n=1, and Y=2 then X = 2 then
2-1>= 2 false

Let n=2, and Y=2 then X = 4 then
4-1>= 2 true

Insufficient..

Statement 2:
X/Y>1 means
X>y if X and Y are positive and X<Y if X and Y are negative

Let X= 3 and Y = 2 then
3-1>= 2 true

Let x= -10, then Y has to be greater than X , so let Y be -5
-10-1>=-5 false..

Insufficient..

Statement 1+2

From 1 we have that X is positive and From 2 , if X is positive than Y also has to be positive and now plugin any values you will get x-1>=y
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by moonraker » Sun Oct 16, 2011 11:09 am
statement 1 says : x is a positive multiple of y => implying that both x and y are positive.
Now multiples of y can be y, 2y, 3y , 4y and so on.

Now replacing these multiples in place of x.

Save for the first option multiple = y, all others satisfy x-1 >= y .

So we have 2 answers based on the value of y we choose...................... so statement 1 is not sufficient alone.

Statement 2: x/y > 1 - ----- this again is insufficient. x and y can be both positive and negative.

Now combining statement 1 and 2 we see that if x/y > 1 then x and y being positive (inference from statement 1) x > y.

Hence x can be any multiple of y but y.

hence both statements 1 and 2 are needed to solve this problem
Last edited by moonraker on Tue Oct 18, 2011 6:10 am, edited 2 times in total.
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by thestartupguy » Mon Oct 17, 2011 9:08 am
IMO:B

Statement 2: x>y
Consider x=-2, y=-3 => x>y
So, Substituting values of x and y, x-1=y which is given in the condition
If x is very large than y, then x>y.

So answer is B
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by Brian@VeritasPrep » Mon Oct 17, 2011 11:44 am
moonraker nailed it, but since we had a few "B" answers on this thread let me make sure to clarify:

B is the trap answer on this question, with the trap being "what about negative numbers?". That's an extremely common trap, so remember it:

**When a Data Sufficiency involves an inequality, the most likely trap is that you'll forget about negative numbers**

And the most common way they do that is to include a variable by which you'll multiply or divide. Here, statement two gives us two possibilities. For x/y to be greater than positive-1, then x and y are either both positive or both negative, so we could have:

Both Positive: x = 4, y = 1, x/y = 4/1, and x-1 is still greater than y. So.. "YES"

Both Negative: x = -4, y = -1, x/y = 4/1 (so the statement holds) and (x - 1) = -5, which is LESS THAN -1 (which is y). So... "NO"

But then statement 1 comes to save the day - because it tells us that x is positive, then we know that both x and y are positive, so the negative "trap" is no longer available. That's why the answer is C.
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep

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by thestartupguy » Fri Oct 21, 2011 2:49 pm
Hi Brian,

Can you please clarify the Statement 1, which reads 'x is a positive multiple of y'

So, x = ky k>0

Can I say x = -6, y = -2 and still k is positive and is equal to 3. If this is true it will still bring in the negative values to the discussion.
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