Of course you have to take the statements separately. This is easier said than done. In practice, I've actually held up a piece of paper over the computer screen to cover the statement I'm not working on.
It would also help for you to create an error log
so you can figure out what specifically about DS questions trip you up.
Is it that you're answer B, that the 2nd choice is sufficient but using information from statement 1 to make it sufficient so the correct answer is C?
Are you answering that one is sufficient while the other is not, but then there are cases that make the answer not true. Somtimes the question might have variables x & y. We grab 2 numbers to see if those numbers work for an equation in the stem and the equation given in a statement. If those numbers work, we have to keep trying to find numbers that do not work so we can say with certainty that #1 is or is not sufficient.
The structure of DS is a difficult way to approach a math problem because you're not actually answering a math problem. You're using math to answer a completely different question. The qusetion is testing your ability to recognize what information is necessary to solve a problem and then filter out the information given to you and seeing if you have enough. They may use math to figure it out, but it's problem solving and analysis with math as the means rather than the end.
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.