Solving DS questions

Hello, monikakumar. I just practiced a mixed question set earlier of PS and DS problems, and I know what you mean. Do you have to write everything down? No. Looking at my scratch pad from earlier, I see a lot of random numbers and letters jotted down. However, you definitely want to take account of exactly what information is given and exactly what the question is asking. (Do not assume an unknown is an integer, for example, if that word is not present.) I often write down intermediary numbers to prevent overloading my working memory, not to mention to simply keep all my facts straight. I like to attack the easier-looking statement first and think of a logical split between AD/BCE (if I start with Statement (1)) or BD/ACE. To be honest, sometimes Statement (2) just looks simpler, and I would rather narrow the answer pool using a simpler approach than hack through a tougher statement that might leave me unsure and then move on to the other statement just because it was there. Getting a little momentum going is important on tougher questions, but that is hard to do if you are operating completely on gut instinct.

As for theory, you should check out the topic-by-topic Ultimate GMAT Quantitative Megathread for reference. As another member noted above, you cannot really count on seeing x-number of content-specific DS questions, so a broad approach to your studies would serve you best.

If you have further questions, feel free to ask. Good luck with your studies.

- Andrew

Thanks all for your response. is practising all questions from og will be enough?

It really depends on your target score, monikakumar. Many students rush through OG questions without a firm foundation in theory, and then they find themselves in a bind looking for high-quality questions. Note, too, that the OG does not exactly order the questions for you by content, and many students find it useful to drill the same concept over and over to increase proficiency or achieve mastery in a certain topic. I think at the very least, you should consider supplementing your OG questions with those from the GMAT Club forum, since the latter do provide content-specific threads. I just want to spare you the frustration of exhausting the OG, making the same mistakes in problem after problem, and then feeling as if you cannot get your hands on questions that truly mimic those you will see on the test.

If you have further questions, feel free to ask.

- Andrew

Hello Monika,

The first thing I advise students to do when I start teaching Quant for any competitive exam is to quit doing mental math and put pen to paper. Does this mean that you have to do every single calculation on paper? That would be a clear NO.

You need to be prudent to understand that there’s a thin line between the two.

Do you want to solve a quadratic equation in your mind? Maybe, maybe not.

What about a hard question (irrespective of DS or PS) on Inequalities / Remainders? Definitely not.

What about multiplying two numbers/finding out the LCM or HCF/ squares/adding numbers? Go ahead, by all means.

A lot of times, students end up flipping the above line items on its head and end up doing mental math with the equations/expressions while doing the simpler calculations on paper. Really, it should be the other way round, isn’t it?

I would recommend jotting down important information from a DS question as you read the question.

This will ensure that you don’t spend extra time on FIRST reading the whole question and then coming back to take down information.

It will also ensure that it slows you down and calms your nerves.

Added benefit is you will have all the information you need in front of you to break down the question stem and frame equations/expressions/inequalities.

Last, but not the least, it will reduce the number of wrong assumptions that students very often make when solving DS questions mentally.

As you write down information and start solving the question, write down the options on one side of the scratch paper. Cross out the wrong answers as you eliminate them. This way, you will not have to remember which options have not been eliminated. This will reduce your mental effort and time taken.

In topics like Time & Distance, P&C, Probability, Overlapping sets and Geometry, putting pen to paper is inevitable. The more you write, the better chances of you getting the answer right.
So, I hope that answers your main question on whether you should try to solve DS questions mentally. The answer to that is a clear NO.

On topics like percents, TSD and rates, use your knowledge of numbers and ratios along with the fundamental concepts related to that topic to develop cases. Write down the cases (see, writing comes up again) and then solve the problem. Going by your main question, I have a feeling that you are actually trying to solve them mentally. Also remember to strengthen your concepts in these areas because all these topics are concept-oriented.

The last question of yours is probably the hardest one to answer because I do not have one. I wish I could tell put a finger on a particular topic which gives more questions than the others, but clearly, that’s impossible to do on a test like the GMAT.

Hope that helps!