Qustion from Manhattan GMAT inequalities book

[harshpamnani]

Question : Data Suficiency : What is X
1) X = 4Y-4 (2) XY =8

By solving these 2 equations, I am getting 2 values of X = -8,4
But the answer is E i.e. both equations are not sufficient.

Please guide.

This is Ques 15, Page 49, Book : Inequalities

[messi10]

Hi,

With data sufficiency questions, you need to have one value only. If you are getting more than one value after taking the two statements together, then it is considered insufficient.

This is slightly different from what you may have learnt in school where equations that give values are considered solvable. But data sufficiency, you need to be able to answer the question without ambiguity. Two values of x does not answer the question "What is x?" in data sufficiency.

Regards

Sunil

[jnelson0612]

Great explanation, Sunil.

BTW, going forward these types of questions should be posted in our forum for the Math Strategy Guides: manhattan-gmat-math-strategy-guides-f7.html