Why Patience Pays off on Data Sufficiency Questions

By - Mar 21, 14:35 PM Comments [6]

By Jen Rugani

In the Nintendo game Super Mario Bros., Mario uses green warp pipes to travel around the world. Even though some of these pipes don’t lead anywhere, savvy players know that it’s wise to try to enter every single one, because every so often, one transports Mario to a room full of bonus coins. Score!

I’m often reminded of this warp-pipe bonus when tackling a tricky DS question. Taking a few seconds to make a little extra effort can generate huge returns; in data sufficiency, this means spending some time with the prompt to simplify the question before moving on to the statements. Let’s take a look at this example:

If xy, and z are negative numbers such that z = 40x + 80y and xy = -1, is z < -60?

  1. xy
  2. y < -0.5

Many test-takers will see a problem like this and immediately start working with the number properties and testing cases. Could this get you to a correct answer? Sure, but look what happens if we give the warp pipe a try and spend some time with the prompt first. I’d rather work with two variables than three (especially since I only see x andy in the statements), so first I’ll substitute 40x + 80y to replace z in the question inequality.

Now the question becomes

Is 40x + 80y < -60?

I know that x y = -1, so now I want to manipulate the inequality in such a way that I can make another substitution. If I divide both sides by 40, I get

Is x + 2y < -1.5? or, more helpfully, Is x y y < -1.5?

Now I can substitute -1 for xy to get

Is -1 + y < -1.5?

Add 1 to both sides, and we can see that this question really becomes

Is y < -0.5?

That’s so much simpler than the given prompt, and looking at Statement 2, I can immediately see that the GMAT has given me a room full of bonus coins to reward my work! Is y < -0.5? Why yes, it is – an easy, immediate sufficient. Moving on to Statement

1, I’m still looking for opportunities to substitute with info from the prompt, so I add y to both sides to get

xy > 2y

Now I can substitute -1 on the left side

-1 > 2y

And finally, divide both sides by 2

-0.5 > y

Done! Another straightforward sufficient, and I can answer D with confidence. This is a question that seems much more difficult than it really is – as we can see, the GMAT rewards test-takers who are patient enough to work with the prompt before moving on to the statements. Take advantage of opportunities to simplify the question, and your room full of coins awaits!

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[6] Comments to this Article

  1. mk March 22, 8:29 AM

    I like the method. Will surely try to incorporate it in my practice.
    Thanks.

    Reply

  2. sudhir March 22, 11:43 AM

    its too good, please post more such question

    Reply

  3. Thimmu March 22, 4:08 PM

    Very informative. Thank you..

    Reply

  4. Nishant March 27, 10:17 AM

    That was really a hard run turned into a cake walk….But for this kind of approach you need to be calm at the time of taking test, otherwise you would keep on adding and subtracting instead of simplifying the given data….

    Reply

    1. Nishant March 27, 10:18 AM

      And i forgot, thanks a lot…this was indeed very helpful for me who always (unluckily) gets stuck up in the long way

      Reply

  5. sonia August 7, 2:55 PM

    Moving on to Statement

    1, I’m still looking for opportunities to substitute with info from the prompt, so I add y to both sides to get

    WHERE DOES THIS COME FROM?
    x + y > 2y

    Reply