Way back in 2005, Kaplan was using a 12TEN mnemonic (kudos for spelling) to help teachers help students to understand the meaning behind the answer choices in Data Sufficiency questions.
This is still a handy way to memorise those answer choices, which do not change from question to question. Quick recap: 1 stands for Option 1 Only, 2 for Option 2 Only, T for Options 1&2 Together. E for Either 1 or 2 Alone, and N for Neither 1 nor 2.
As an aside, back in elementary school they taught us a rule of spelling, "i before e, except after c." It was only thanks to the GMAT that I learned, much later in life, that to every rule there is at least one exception. The phrase, Data Sufficiency, is one such exception. Science is another. Don't know how I missed that, as a bright-eyed eleven-year-old....
But to return to the main event, the meaning behind the DS answer choices is only the very tip of the iceberg. It may or may not be obvious to you, but workflow is the single biggest factor affecting DS performance. It is like the pit crew in a motorcar race, a Formula 1 race, if you will. No matter the mathematical power that you bring to the table, or to the race, you will indubitably lose much time, if not make straight-up mistakes, because of your workflow.
The first and most serious mistake is called Seepage, or Leakage, or Bleeding. It has no fixed name, to my knowledge, but Manhattan GMAT is probably able to think up a good one, now that they know about the topic. Yes, as an aside, I do have a gripe with that old lighthouse on the GMAT shores. They once flew me out to New York, heard my ideas about divisibility, and then wrote them into their book series and waved me goodbye. Well, now I am waving back, and later in this post you will see why their DS framework is like a pair of ski boots in a mud-wrestling match. Or, better than showing that, I will wait for their Presidential Nominee Wannabee to fly me out.
But to return to the main event, the meaning of 12TEN really is an important first step. Kredit goes to Kaplan, who by the way bought out Manhattan, some years ago, thus allowing senior staff to vie for the White House. The second step is to memorize the geographic location of these answer choices. The very letters ABCDE should be synonymous both with 12TEN and with the relevant positions on the screen: Together=C=Third needs to be hard-wired in.
Third step, stabilise your workflow. Check out the implications of Fact 1, henceforth termed F1. Is F1 enough, or not enough? Decide. Do not bounce down to Fact 2, or F2. A solid test taker can bounce around - even should. But make sure you are one of those, and in the meantime stay humble and work from F1 to F2, without fail. Build the habit. Otherwise you are at worst Toast, and at best Progress Long Delayed. Every Data Sufficiency question is set up to tempt you and delude you into doing blending your assumptions. The two facts, Fact 1 and Fact 2, or F1 and F2, are two totally utterly independent facts. Looking at the one means ignoring the other. Do it.
Fourth step, if necessary, is to combine F1 and F2. This is to be done only when both facts alone were of no use to you. It's like Peanut Butter and Jelly: the Dutch love Peanut Butter; the English love Jelly; but true blue American patriots know - even in childhood - that you need them both to make a Peanut Butter & jelly Sandwich.
Finally, I have a drawing. It is much better than text.
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