There could be 4 possibilities:
X = +ive, Y = +ive
X = +ive, Y = -ive
X = -ive, Y = +ive
X = -ive, Y = -ive
On looking at both the equation, I guessed that 3 and 2.5 could be best substitute for the +ive & -ive values of X and Y.
Condition 1: 2x - 2y = 1
So on applying it the above situations we get,
(X = 3, Y = 2.5) satisfy the equation.
(X = 3, Y = -2.5) does not satisfy the equation.
(X = -3, Y = 2.5) does satisfy the equation.
(X = -2.5, Y = -3) satisfy the equation.
so by condition 1, we come to know that either both x and y are positive or both are negative. (NOT SUFFICIENT)
Condition 2: x/y > 1
So on applying it the above situations we get,
(X = 3, Y = 2.5) satisfy the equation.
(X = 3, Y = -2.5) does not satisfy the equation.
(X = -3, Y = 2.5) does satisfy the equation.
(X = -3, Y = -2.5) satisfy the equation.
so by condition 2 also, we come to know that either both x and y are positive or both are negative. (NOT SUFFICIENT)
Now lets take both the condition together:-
The last case that is both x and y are negative are contradict to each other in condition 1 and 2, so x and y could not be negative. (Check carefully)
Hence, to satisfy both conditions x and y should be positive only.
Hence answer is (C)
GMATPrep DS - 6
This topic has expert replies
Source: Beat The GMAT — Data Sufficiency |
-
codesnooker
- Legendary Member
- Posts: 543
- Joined: Fri Jan 18, 2008 1:01 am
- Thanked: 43 times
- GMAT Score:580
-
camitava
- Legendary Member
- Posts: 645
- Joined: Wed Sep 05, 2007 4:37 am
- Location: India
- Thanked: 34 times
- Followed by:5 members
codesnooker, thanks for your input! But I am not getting one thing -codesnooker wrote: Now lets take both the condition together:-
The last case that is both x and y are negative are contradict to each other in condition 1 and 2, so x and y could not be negative. (Check carefully)
Hence, to satisfy both conditions x and y should be positive only.
Hence answer is (C)
Initially when u took the condition-1 with the examples, u assumed X = -2.5 and Y = -3 - which holds the condition-1.
But when u tried to take the condition-2 in account, u mentioned X = -3 and Y = -2.5 - This assumption obviously will not validate the condition-1.
So why C? Am I missing something?
Correct me If I am wrong
Regards,
Amitava
Regards,
Amitava
-
codesnooker
- Legendary Member
- Posts: 543
- Joined: Fri Jan 18, 2008 1:01 am
- Thanked: 43 times
- GMAT Score:580
I switched the values because initially I want to prove that both statements alone true for negative values along with positive values. --> Only to make both statements as NOT SUFFICIENT.
Now, when we taken both statements together, the equations contradicts (oppose) to each other for negative values. It means if keep same negative values for both the statement, one will hold true and other will not. So, it means x and y can never be negative, as for negative values one is true and another is false.
Only if both X and Y are positive, then both the condition satisfied. Hence both statements together are sufficient to depict that both X and Y should be positive numbers (not integers) and alone none is SUFFICIENT.
Hope you get the logic now.
Now, when we taken both statements together, the equations contradicts (oppose) to each other for negative values. It means if keep same negative values for both the statement, one will hold true and other will not. So, it means x and y can never be negative, as for negative values one is true and another is false.
Only if both X and Y are positive, then both the condition satisfied. Hence both statements together are sufficient to depict that both X and Y should be positive numbers (not integers) and alone none is SUFFICIENT.
Hope you get the logic now.
-
codesnooker
- Legendary Member
- Posts: 543
- Joined: Fri Jan 18, 2008 1:01 am
- Thanked: 43 times
- GMAT Score:580
Yes, initially it confused me for a second, then I closed my eyes and taken a deep breath and looked on the question. I got the logic in next second. 
-
netigen
- Legendary Member
- Posts: 631
- Joined: Mon Feb 18, 2008 11:57 pm
- Thanked: 29 times
- Followed by:3 members
Another approach:
B) X/Y>1 or |x|>|y| insufficient X=-3 and Y=-2
A) 2X-2Y=1 or x-y=1/2 insufficient X=-2 and Y=-2.5
Together: sufficient because for negative values for A to be true |x|<|y| always
B) X/Y>1 or |x|>|y| insufficient X=-3 and Y=-2
A) 2X-2Y=1 or x-y=1/2 insufficient X=-2 and Y=-2.5
Together: sufficient because for negative values for A to be true |x|<|y| always
