Quantitative Section Made Easy: Data Sufficiency
Here we cover material that will show up in the Quantitative Section of your GMAT, so if you want to do well on your GMAT and get into that MBA program, you better review this stuff. We now move away from the regular Problem Solving questions and think about the Data Sufficiency ones.
» Data Sufficiency? Oh my…
Let's go over the basic concepts of the data sufficiency problems. These represent about half of the problems in the Quantitative Section. Data sufficiency problems consist of a mathematical problem, and 2 statements containing data. Then you have to choose one of the 5 different answer choices regarding which of the 2 statements is sufficient for you to answer the problem. The answers will always be:
A. Statement 1 ALONE is sufficient but statement 2 alone is not sufficient.
B. Statement 2 ALONE is sufficient but statement 1 alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement alone is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements 1 and 2 TOGETHER are NOT sufficient.
» It's example time
What is ?
1.
2.
(The answer options are the same as above)
Well, statement 1 can't help you figure anything out on its own, since it's an equation with 2 variables. Statement 2 can't help much either - there's no y in there. So we cancel out options A, B and D. Now think - can we use the two together to find y? Yeah, we can. From 2 we can find x, and plug it into 1 to get y. So the answer is C.
» OK, so how do we solve these?
Here are a few simple steps you should follow:
1. Ignore statement 2. Can you solve the problem just with statement 1? If so, the answer is either A or D. Otherwise, it's B, C or E.
2. Now, forget statement 1. Can you solve the problem just with statement 2? If so, and if the answer to the question above was yes, D is your answer. If the answer from above was no, the answer is B. If you can't use just statement 2 but can use 1, it's A. Otherwise, move on.
3. If neither question alone works, try using both. Are you good now? The answer is C. Not good enough yet?
It's E.
That's all you need to do to figure out the answer. You don't have to actually solve the questions, but sometimes you may find yourself forced to do that if you're not sure of what's going on. It's always simpler to try to solve a problem, but you may have to do that 3 times per question, first using just statement 1, then just 2, then both.
» Trickery and treachery - The yes/no data sufficiency
These are very confusing questions with the sole purpose to throw you off track.
For example: Is an integer?
1. is a positive
integer.
2.
Think. Is statement one enough to answer the question? If 2x is a positive integer, x may be 2. It may also be 1/2. Which one is it? We don't know. So statement 1 is not sufficient. If you have 2 possible conflicting answers you may think it's a good thing, but remember that you're trying to figure out what the definite answer is. Don't be tempted to say statement 1 is sufficient here.
How about statement 2? Well, clearly in statement 2 x is not an integer. STOP! If you're thinking, ok, neither statement can help me, you're wrong. With statement 2, the answer is no, but it's an answer. You CAN answer the question with statement 2. Thus, the answer to this problem is B, not E. See how confusing this is?x%x
Once again, remember what the question is asking- not for you to solve the problem, but to determine whether information is sufficient to solve the problem, whether the answer to the problem is 5, -1992834, yes, or blue.
» Any tips or suggestions?
Remember that the problems in data sufficiency are on the same topics as the regular problems, so if you know your stuff you're already halfway to a solution.
1. Got equations in your statements? Remember that one-variable equations most often give you one solution, quadratics may give you 2, and two-variable equations cannot be solved on their own.
2. Got huge exponent questions? Remember your exponent laws that may cancel some variables out, causing them to be unnecessary for a solution.
3. A geometry problem? Use the diagram. Always look at the angles and sides you know before looking at the statements, and ask yourself "which angles do I need here to find what's I'm looking for? Which other angles or sides can allow me to find them?"
4. Never assume anything. If a question asks you about option A with a statement talking about option B, the statement may not be sufficient- don't assume there is no option C you weren't told about.
5. Can you only figure one statement out? No worries. Knowing whether one statement is sufficient to answer the question is enough to cancel out at least 2 choices. You're already at a guessing position now, so even if you have no idea of what the other statement is saying, you have a chance at getting it right.
And that's all. If you've read the previous 2 lessons and practiced all of your stuff, you are now ready to face the Quantitative Section of the GMAT.
Good Luck!
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