In your example, for statement 1 you got just one value for x, and that value was 2, and for statement 2 you also got a single value but it was 3. So each statement gives you just one value and this appears to be choice D, but the statements contradict each other. And you noticed that the official answer to these questions is not D. So you said

So, can I deduce from getting two different values (from each statements independently) that I did a mistake?

The answer is "yes." You made a mistake.

If you get different values from the two statements in data sufficiency then the answer is not "D." In fact, I refer to this as "answer choice F." Because if you the statements have no way to agree with each other you should not pick any answer (a - e) you should instead try to learn where you made you mistake.

You see, data sufficiency is like problem solving. There is an actual value for each variable. Since you are working with just one problem (even though there are two statements) there is just one actual value for x (or y or z, etc.)

In short, the statements in data sufficiency must never completely contradict each other. This is because the statements are never wrong, they are only perhaps not specific enough.

I wrote an article on this very subject that I would like for you to read. https://www.beatthegmat.com/mba/2012/01/ ... ufficiency

The article will tell you how you can apply this knowledge on test day in order to catch errors that you may have made.

Hope it helps!

Thanks David!!


Your explanation makes perfect sense.now I have further "tool".
Thanks again for confirming.

Great to see you picking up on that. Most students never see the pattern without having it explained. Let me know if you make any other observations on Data Sufficiency. Data Sufficiency theory is perhaps my favorite subject.