Stop SOLVING Data Sufficiency Questions

Say it's 9:40 on a Tuesday night. The kids are finally asleep, the laptop is open, and you're working a Quant question on the couch. You set up two equations. You solve them. You check your arithmetic. You get 18. You feel great. You pick your answer.

Three and a half minutes, gone. And here is the painful part: the test NEVER wanted the 18.

That was a Data Sufficiency question. If you're solving those all the way to the end, you're doing math that nobody is grading. You're a working professional with a job, a family and maybe an hour a night to train. You cannot afford to give away minutes. Let's fix this.

What Data Sufficiency actually asks

The Quantitative Reasoning section of the Executive Assessment gives you 14 questions in 30 minutes, according to GMAC's page on the test structure. Some are Problem Solving, the normal "find the answer" kind. The rest are Data Sufficiency, or DS. A DS question gives you a question plus two facts, called statements. Your job is NOT to answer the question. Your job is to decide whether the statements give you ENOUGH information to answer it. That's all "sufficient" means: enough.

Every DS question uses the same five answer choices:

• (A) Statement (1) ALONE is enough, but statement (2) alone is not.
• (B) Statement (2) ALONE is enough, but statement (1) alone is not.
• (C) BOTH statements TOGETHER are enough, but neither one alone is.
• (D) EACH statement alone is enough.
• (E) Even together, the statements are NOT enough.

Read those again. Not one of them is a number. The test never asks what x equals. It asks whether you COULD find x. Those are two very different jobs, and one of them is a lot faster.

Now do the clock math. 30 minutes for 14 questions is a little over 2 minutes per question, on average. Every minute you spend finishing an equation the test won't grade is a minute you steal from a question you could have gotten right. And since each section is scored 0 to 20, and all three sections count the same toward your 100 to 200 total, those Quant points matter just as much as anything else on the test.

I'll bet the last DS question you did, you solved all the way to the final number. Go look at your notes. Be honest with yourself.

The only question that matters: ONE answer, or more than one?

Here's the whole game, in one line. A statement is sufficient when it locks you into exactly ONE answer. If you can find two different answers that both fit the statement, it's not sufficient.

That works for value questions like the one above. It also works for yes or no questions, and that's where TESTing VALUES does the heavy lifting. Instead of trying to prove something with algebra, you plug in real numbers and watch what happens.

5 mistakes I see people make on DS every week

1. Solving to the final number. You found a way to get the answer, then kept going anyway because stopping felt like cheating. INSTEAD: the moment you KNOW you could get one answer, stop. Write "yes" next to that statement and move to the next one.
2. Doing DS in your head. DS feels "light" because there's less math, so people skip notes. Then they forget which statement they already decided on, or mix them up. INSTEAD: write a tiny grid on your noteboard: "AD" on one line, "BCE" under it. If statement (1) is enough, cross out BCE. If it isn't, cross out AD. Then statement (2) decides between what's left. Paper never forgets.
3. Letting statement (1) leak into statement (2). You learned something from (1), and it sneaks into how you read (2). That's how people pick D when the answer is B. INSTEAD: judge each statement ALONE first. Literally cover the other one. You only combine them if neither works by itself.
4. Thinking a "NO" answer means not enough. If a statement tells you the answer is ALWAYS no, that's one answer. That's sufficient. INSTEAD: ask "Is the answer always the same?" not "Is the answer yes?" A sure NO counts just as much as a sure YES.
5. Trusting "two equations, two unknowns" without looking. It's a great shortcut, and it fails in one spot: when the second equation is just the first one in disguise. 2x + 2y = 10 and x + y = 5 are the SAME equation. INSTEAD: take two seconds to check that the second equation isn't the first one multiplied or divided by some number. If it's truly different, you're done.

Why this is training, not knowledge

None of this is new math. You already know how to solve two equations. The hard part is the habit. Your whole career has rewarded you for finishing the job, for getting to the number, for checking your work twice. On DS, that instinct costs you. You have to train yourself to stop on purpose, the same way a sprinter trains to run THROUGH the line and not past it.

So you have to decide what you want MORE: the satisfying feeling of seeing 18 on your paper, or two extra minutes for the question at the end of the section that you'd otherwise have to guess on.

Here's your job for today. Pull up 10 DS questions you've already done. Redo every one with a timer running. On each, write the AD/BCE grid, judge each statement alone, and STOP the instant you know whether one answer is possible. Write your time next to each question. Then compare it to how long those same questions took you the first time. If the new times aren't clearly faster, look at your paper and find the exact spot where you kept solving after you already knew.