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What's your DS approach?

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What's your DS approach?

by cbenk121 » Tue Oct 27, 2009 7:58 pm
Hi all,

I've been doing well in PS problems, but not so great in DS. Because i was advised not to actually "solve" the problem, I try to mentally figure out whether each statement is sufficient.

While I never carry information from statement 1 to statement 2, I do tend to make careless mistakes...usually assuming E when it's C or assuming it's C when it's A or B (i.e. leaning toward assuming it's not sufficient).

I'd like to figure out a more careful approach. I'm sure I need to write some of the problem down, but I'm afraid of writing down too much (i.e. solving the problem).

How do you all approach DS problems? Would like to get a few ideas to try as I head into more intermediate/difficult DS problems. Thanks!

Edit: This link basically says practice, which I'm planning on once I get a few ideas :) https://www.urch.com/forums/gmat-data-su ... lp-ds.html
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by Testluv » Wed Oct 28, 2009 10:59 pm
Hi cbenk121,

Not surprisingly, I think the remedy has to do with method and technique...and not surprisingly I will endorse the Kaplan method.

Step one of the Kaplan method for data sufficiency:
Focus on the Question stem.

Here, we determine whether the question is asking for a value or a yes/no response, stock up our information (if any) in the actual question and make deductions (if possible). We also translate english into equations (if there are translatable sentences). There are two other things we do here. We ask if we can rephrase or simplify the problem. This is because there is often a simpler question residing underneath the one being superficially posed. For example, "is (m+n)/2 an ineger?" can be rephrased as "is m + n even?" Yes/no questions can often be simplified. Most importantly, we determine what information is necessary for answering the question. This is because for information to be sufficient that information has to provide us with all pieces of information that would be necessary for answering the question.
(Now, I'm not saying we have to do these things in the order I discussed them or that we have to do all these things all of the time. )

Step two: determine the sufficiency of each statement independently from each other but in conjunction with the information in the question stem. Start with the easier statement first. If both look equally easy (or equally hard), start with the first. Remember that the statements are both true so if you pick numbers you have to pick numbers that satisfy them. Remember that the statements never contradict each other.

Step three: Combine the info in the two statements only if necessary (ie, only if each statement was independently insufficient). When combining treat the info in the stem and both statements one big problem and see whether you have sufficiency or not.

Have a system for eliminating answer choices. And practice it with pretend statements (no actual question required).

Know that the most important tactic in data sufficiency involves simply counting the number of equations and the number of unknowns (I posted on this tactic just yesterday in the data sufficiency forum).

When reviewing, make sure you review not just your wrong answers but also your right ones. Because we want to get better at refraining from doing math when unnecessary, when reviewing your correct answers ask yourself: what is the first point in my thinking that I should have (or could have) seen that the statement was (or was not) sufficient. What calculations could I have avoided?, etc.

When reviewing your wrong answers, examine your assumptions carefully. Here (during review of wrong answers, that is), it is often a good idea to actually do the math in order to examine more critically your assumptions (so that you don't make those assumptions on test day!)

When reviewing, try not to go straight to solutions. Instead, try to figure it out on your own, referring to other problems and/or GMAT help books. Look for where the same concepts are being tested in slightly different ways and where slightly different concepts are being tested in the same way.

Finally, be bold.
Kaplan Teacher in Toronto
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