mevicks wrote:Brent@GMATPrepNow wrote:
Statements 1 and 2 combined
IMPORTANT: If b/d > 0 (statement 2), then EITHER b and d are both positive, OR b and d are both negative.
Cheers,
Brent
Hi Brent,
I stopped after reaching the conclusion that both b,d can be negative or positive. And in order to save time quickly chose [spoiler]E (incorrect answer here)[/spoiler] "hoping" that they have no role in the combined statements since a and c are still unknown.
However after reviewing my error I did understand that my mistake was not going that extra step to check and verify the solutions together. I'm prone to similar problems in complicated DS questions where we have to take that extra leap, for eg:
Stem : What is x ?
St.1: |x+3| = 4x - 3
Ans: St. 1 is sufficient since x = 2 or x = 0, but x = 0 does not satisfy the equation so x = 2 is the only answer, thus sufficient.
Same is the situation with deadly DS+Quadratic equations.
My question is do we make it a rule of thumb to recheck and reverify ALL DS answers by plugging in the final values if possible?
Thanks & Regards,
Vivek
I'd say don't confuse intermediate goals with the actual target question.
When we encounter a DS question, we often begin imagining what kind of information would be sufficient to answer the target question, and we can get into trouble by confusing this intermediate goal with the actual target question.
For example, if a target question asks us to find the value of x², we might think, "
To answer this question, it would be sufficient if I knew the value of x" (So, the intermediate goal is to find the value of x, even though this is actually more information than is really needed). From here, you might check one of the statements, and it leads you to the conclusion that x equals EITHER 3 or -3. At this point, you might think, "
That's not enough information, because I want to find the value of x." This is what I mean by confusing an intermediate goal with the actual target question. If the goal were to find the value of x, then the statement would, indeed, be insufficient. However, since the goal is to find the value of x², the statement is sufficient (since 3²=9 and (-3)²=9).
Likewise, for the original question, we have two possible scenarios for the variables b and d, but this does not necessarily mean we have two possible (and different) answers to the target question.
I hope that helps.
Cheers,
Brent
