A Data Sufficiency How To
The data sufficiency is really unlike any other type of math question. You don’t actually answer the math question, rather you must determine if you have enough information to answer the question. These style questions do not require any skills beyond those needed for the other math on the GMAT. Given the unique nature of this type of question, you should practice them and familiarize yourself with the directions. We discussed them in this previous post. The main purpose of these questions is to lure you into making an unwarranted assumption.
The first thing you should do when you see a data sufficiency question is list the answer choices as follows. (We’ll get to why this is important in second):
AD
BCE
Additionally, the initial information given can often be presented in a convoluted manner. If you can translate this into something more easily decipherable, you will help yourself. For example, if one of the conditions is X is a factor of Y, you can rewrite this as “Y/X is an integer”. 3x=9y can be simplified to x=3y.
If you see a question like this, you should manipulate it as best you can into a simple algebraic expression.
Is x divisible by 2? Can be expressed as: Is x even?
Is X greater than 0? Can be rephrased as: Is x positive?
Once you have simplified the initial information, look at statement 1. Can you determine the answer to the question? Remember, you do not need to solve the problem just evaluate if you have enough information to calculate an answer.
If Statement 1 is sufficient, cross off BCE as there is no way any of those choices could be the correct answer. If you find that you need more information after evaluating the first statement, cross off AD as neither of those answers can be correct.
Once you have eliminated several answer choices, look at statement 2 independently. Using only the information in statement 2, determine if there is enough information to answer the question. Based on your answer, you should be able to cross off more answer choices.
If neither statement provided sufficient data independently, try to solve the problem using the information in both statements. You can then determine if your answer is C (combined, the two statements provide enough information) or E (not enough information).
If you are being asked to solve for a variable, remember you must have as many expressions or algebraic sentences as you do variables. To solve for X, you only need one statement with the one variable X in it. If you have two variables, you need two independent statements to determine the values of each variable. Three variables would require three statements, and so on. Be careful, though, because the test writers like to trick people into thinking they have two distinct algebraic statements when they really don’t. We’ll cover this trap in a later post, so stay tuned.
Remember – practice, practice, practice – and it will get easier!
Add comment April 10th, 2008