elegan wrote:
Statement 1)
If k > 0, well it shouldn't matter what k is, so I thought this was okay, so I thought statement 1 is true.
Dear
elegan,
Everyone else on the page said that you were wrong, but it's not clear to me that anyone explained in clearly enough so that you now fully understand the deeper issue at play here.
I'll begin by saying, here are a couple blogs you may find informative about DS in general.
http://magoosh.com/gmat/2012/introducti ... fficiency/http://magoosh.com/gmat/2012/gmat-data- ... trategies/You made a very classic DS mistake ---- confusing the "truth value question" with the "sufficiency question."
The prompt in this question is: "
Is the value of expression k – m + 1 greater than the expression k+ m – 1?" That's a 'truth value question", about whether a mathematical statement is true or false. Technically speaking, we are not answering this question at all. Technically, our job on DS is to answer the "sufficiency question" --- viz., given this new piece of information, the DS Statement, would this piece of information allow me to determine a definitive answer to the prompt question?
When you look at a DS statement, your job is
not to answer any of these questions
"
is this true?"
"
could this be true?"
"
would it be OK if this were true?"
"
is this consistent with the prompt?"
Rather, your job is very focused and specific: your job is to answer the single question
"
Is this statement sufficient?"
i.e.
"
If I were given this statement as a true piece of information, over and above whatever true pieces of info I have from the prompt, does this allow me to determine a definitive answer to the prompt question?"
All of math depends on precision. In DS, part of success is making sure that you are
always answering the sufficiency question, and never any other question, when you evaluate these statements.
If you are considering a different question than the one you are supposed to consider, you will tend to get DS questions incorrect. For example, in this case, recognizing the value of K doesn't matter would lead to a resounding "yes!" if we were working with something like the question "
could this be true?", but if we are working very strictly with the sufficiency question, irrelevance generally does not help us at all in determining anything definitively. If we focus precisely on the sufficiency question, we must arrive at a "no" answer here ---- statement #1 is
not sufficient.
Does all this make sense?
Mike
_________________
Mike McGarry
Magoosh Test Prep