Doubt in data sufficiency rules

Question

In value based DS questions , is it possible that both statements give unique value but different unique values.
For example

If x+y=6, what is the value of x ?
1)y=2
2)y=3

from 1 we get x=4 and from 2 we get x=3.
Both values of x are different but distinct.

Is it possible to have such questions on GMAT ?
If yes, then what should be the answer, D or E ?

ENGRTOMBA2018 · Answer

Good question but the answer is NO. The 2 statements , if sufficient individually, can not give you 2 contradictory answers. If it is a unique value question, then the unique value MUST be the same for both the statements.

EMPOWERgmatRichC · Answer

Hi kunal555,

Engr2012 is correct - if each of the two Facts is SUFFICIENT, then they must be so for the same reason (re: the same single 'answer' to the question). The GMAT makes NO exceptions on this issue.

To take this a step further, IF you believe that both Facts are sufficient on their own, but they show different answers, then YOU have likely made a mistake somewhere and should double-check your work. To be fair, in that situation, It would also be possible that you were practicing with material that was poorly designed.

GMAT assassins aren't born, they're made,
Rich

dabral · Answer

kunal555

No, such questions do not follow the accepted pattern on the official GMAT questions.

In GMAT data sufficiency questions, the two statements will never contradict each other. It is an unspoken rule on the GMAT that the value of the quantity being asked in the main stem will always be the same in case each statement alone is sufficient. This rule is not explicitly written in official GMAT sources, but is consistently seen in GMAT problems.

You will also see variations of the type listed below:

If x+y=6, then what is the value of x?

1) y^2 = 4 
2) y=2

Here statement 1 is insufficient, and statement 2 alone is sufficient. But note that both statements share a common value of y. This is also a common scenario on data sufficiency questions.

Cheers,
Dabral

kunal555 · Answer

Clear now
Thank you all for your inputs.

chartdude · Answer

This is a dummy example but it demonstrate my question:

Question: What is the value of X?
1) X + 3 = 0 ->>> Sufficient 
2) X + 5 = 6 ->>>> Sufficient as well

In this case, naturally I would choose E: because both are sufficient on it own
But the Dilema is: because they both produce different value, therefore, Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.

So which is E or N the correct answer? (Each or Neither?)

Thanks so you much!

HardWorkBeatsAll · Answer

The answer is D - each alone is sufficient.

Note that you should treat 1 and 2 as being completely independent of each other. Each can yield different values (although GMAT won't test you on such a technicality).

Only in the case that one doesn't suffice should you look at the combination of both.

What is important is - are you able to answer the question asked with the info provided? If so, great. They don't have to corroborate.

So, if each is independently sufficient, that takes priority and you shouldn't even consider what happens when you take them together.

ENGRTOMBA2018 · Answer

Look above for the discussion.

For GMAT DS questions, if both statements are indeed sufficient individually, then they MUST give the same unique value.

Doubt in data sufficiency rules

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