Algebra guide: Question 5 Page 89: Two values of X

[SherryK835]

Hello,
The data sufficiency question asks:

What is x?
1. x=4y-4
2. xy=8

Putting together the two statements, we get a quadratic equation, that tells us that x=8 or x=-4

The answer in the book is E. Is this because there are two values for x?
Does that mean until and unless we can get only one value of x, the statements are insufficient?

What if the question is in a word problem, and x represents the number of oranges. Then in that case it can only be a positive number, so we can disregard x=-4. In this scenario, do we then have sufficient information to determine what x is?

Thanks for all your help.

[RonPurewal]

hi,
if this is a problem from one of our strategy guides, please post it in the "MGMAT non-CAT Math" folder. thanks.