duchessjs wrote:
Bunuel wrote:
SOLUTION
If xy > 0, does (x - 1)(y - 1) = 1?
\(xy>0\) means that either both \(x\) and \(y\) are positive or both are negative (so neither of unknowns equals to zero: \(x\neq{0}\) and \(y\neq{0}\)).
Question: is \((x-1)(y-1)=1\)? --> is \(xy-x-y+1=1\)? is \(x+y=xy\)?
(1) x + y = xy --> directly gives YES answer to the question. Sufficient.
(2) x = y --> question becomes: is \(x+x=x^2\)? --> is \(x(x-2)=0\)? --> is \(x=0\) or \(x=2\)? --> as given that \(x\neq{0}\), then the question becomes is \(x=2\)? We don't know that, hence this statement is not sufficient.
Answer: A.
Hey Bunuel!
When would tautological information come into play? Statement 1, gives no new information. It just restates the information that can already be found in the prompt question.
Magoosh keeps drilling home the idea that a statement providing no new information is considered insufficient. This has burned me several times on
OG questions and causes me to get a simple question wrong. Maybe I'm just not understanding the appropriate situation as to when to use the tautology idea?
I completely understand why your given explanation is the correct answer, but
Magoosh rules keep replaying in my head making me want to mark Statement 1 as insufficient because of its redundancy.
Question:
Is \((x-1)(y-1)=1\)?
----> Is \(xy - x - y + 1 = 1\) ?
----> Is \(x + y = xy\)?
(1) \(x + y = xy\)
<---- Redundant?Hi duchessjs,
Remember, you need to understand that you are working not with two statements but rather with a question and a statement right?
So before discussing this question, let me provide you with an example:
Me : “John, do you want to go to the movies”
John: “Yes, I want to go to the movies”
Notice that John was able to answer the question by REPEATING what I asked him right?
So in this particular problem, the question is:
Is x + y = xy?
Statement one says: YES, x + y = xy
Thus, statement one is sufficient to answer the question.