scottchapman wrote:If L & W represent the length and width, respectively, of the rectangle above, what is the perimeter?

1). 2L+W=40
2). L+W=25

Perimeter of a rectangle with length L and width W = L+L+W+W = 2L + 2W = 2(L+W).
Question stem, rephrased:
What is L+W?

Statement 1: 2L + W = 40
Thus, W = 40 - 2L.

Case 1: L=10, implying that W = 40 - 2*10 = 20.
In this case, L+W = 10+20 = 30.

Case 2: L=15, implying that W = 40 - 2*15 = 10.
In this case, L+W = 15+10 = 25.

Since L+W can be different values, INSUFFICIENT.

Statement 2: L+W = 25
SUFFICIENT.

The correct answer is B.

Scott, this is a good example of a C trap question.

C trap questions are set up to get the test taker thinking that both statements are needed to get to the answer.

In this case, one could be thinking this way. "To calculate the perimeter, I need the length and width."

That thinking might even seem somehow confirmed after working on Statement 1, which allows for multiple values of L and W.

So then you might jump to Statement 2 and find that once again you can't determine the value of L or W.

At that point maybe you notice that you can subtract Statement 2 from Statement 1 and easily calculate the values of L and W. "Ahhhh," you think. "The answer is C."

The thing is that that combining of the statements is not necessary. You don't actually need the values of L and W because P = (L + W) + (L + W). So as soon as you have L + W = 25 you are set. So Statement 2 is sufficient and the answer is B.

If you didn't see that and instead chose C, then you fell into a C trap.

So there's one thing to be aware of in order to do better on DS.

Thank you all for your responses. I struggle with DS and I think part of the reason for it is not rewording the question effectively. It makes sense after I see you guys go through the steps, but for whatever reason, I continue to make the same errors. I'm assuming I just need more practice...

scottchapman wrote:Thank you all for your responses. I struggle with DS and I think part of the reason for it is not rewording the question effectively. It makes sense after I see you guys go through the steps, but for whatever reason, I continue to make the same errors. I'm assuming I just need more practice...

The geometry problem above is a VALUE DS: a DS whose question stem asks for a specific value.
One way to evaluate the statements -- and to avoid falling for a trap -- is to TEST TWO CASES.
If the desired value is THE SAME in each case, the statement is SUFFICIENT.
If the desired value is NOT the same in each case, the statement is INSUFFICIENT.

If L & W represent the length and width, respectively, of the rectangle above, what is the perimeter?

1). 2L + W = 40
2). L + W = 25

Statement 1: 2L + W = 40
Case 1: L=10, W=20, with the result that 2L + W = 2*10 + 20 = 40
The following rectangle is yielded:


Case 2: L=5, W=30, with the result that 2L + W = 2*5 + 30 = 40
The following rectangle is yielded:


Since the perimeter is NOT the same in each case, INSUFFICIENT.

Statement 2: L+W = 25
Case 3: L=10, W=15
The following rectangle is yielded:


Case 4: L=5, W=20
The following rectangle is yielded:


Since the perimeter is THE SAME in each case, SUFFICIENT.

The correct answer is B.

One advantage to this approach:
It does not require any special insight.

scottchapman wrote:Thank you all for your responses. I struggle with DS and I think part of the reason for it is not rewording the question effectively. It makes sense after I see you guys go through the steps, but for whatever reason, I continue to make the same errors. I'm assuming I just need more practice...

You'll definitely get there. Once you get the hang of the format, you may find yourself scoring higher on DS than on PS, even if the questions seem hard. DS is MUCH more guessable than PS, so you can get away with a lot of inspiring guesswork / trial and error / risk intelligence, as opposed to PS where you often need to know the math in question.