Social Distancing with Data Sufficiency Challenge! – Day 21

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This series is designed to help you step up your Data Sufficiency practice while we all spend a little extra time at home during the coronavirus situation; I’m going to publish one practice Data Sufficiency question each day! You can choose to do all of them, or none of them. 

Click on the tag “Social Distancing DS Challenge” at the bottom of this post to see all of the questions in this series! 

And remember to take whatever precautions you need to stay healthy over the next few weeks! 


Question #21

What is the value of x?

(1) 4x + 4 = 0

(2) (x + 2)2 = x2


Explanation

Statement (1) is simple enough to solve with some algebra:
4x + 4 = 0
4x = -4
x = -1: Sufficient.

Statement (2) is trickier. We should multiply it out:
(x + 2)2 = x2
x2 + 2x + 2x + 4 = x2
x
2 + 4x + 4 = x2
4x + 4 = 0
No need to go on, we should recognize this from above. Sufficient!

The correct answer is (D).

Why Paying for a Course (or a Tutor) Isn’t Going to Automatically Get you a 700+

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Sometimes I notice that I get a little push-back when I speak negatively about signing up for certain GMAT courses, buying books, or doing a million practice questions.

And in a sense, it’s understandable.
We want that magical one-size-fits-all GMAT plan that will tell us exactly what to do that we can get a perfect Quant and a perfect Verbal score.

And, don’t get me wrong, courses can be very good. Some GMAT study books are awesome. I constantly recommend videos and books and articles that I find helpful. It’s amazing what’s out there (often for free!) that can help students on their GMAT journey.

And darn it, sometimes, the only way to cement your knowledge of CR Assumption is just to DO a whole bunch of CR Assumption!

BUT I want to discuss an important (and oft overlooked) aspect of GMAT studying that I really don’t see discussed enough: the art of reviewing your own progress. 👈

I have tutored the GMAT for over a decade (I know, it’s a little scary how time flies!), and one thing I have noticed in that time is that students who improve the fastest are not the ones who do the most questions.

So let’s examine a few important ideas and facts that I think can really help anyone working towards their GMAT score reach their maximum potential:

  • Students who improve the fastest are the ones who have the best system in place for reviewing questions. When an automated course “reviews” your questions — all it does is tell you what questions you got right and what questions you got wrong. It doesn’t tell you WHY. And, it doesn’t even require you to put in the elbow grease to find out WHY. And that “why,” my friends, is EVERYTHING!

  • When you don’t know what to do next, look at your most recent CAT/s. Think of yourself like a doctor and your “student-self” is the patient. What is going on with the patient’s GMAT? Is it a lack of content knowledge, or is it more about poor strategy? Perhaps bad pacing management is playing a part?

  • You need to zoom in before you can zoom out. Let’s say you’ve done a couple practice exams, but haven’t really Error Logged them, but you’re scoring much higher in Quant than you are in Verbal. Don’t think, “Hmmm, well I’m not doin well in Verbal, so I’m going to sign up for e-GMAT’s Verbal course and I’m going to buy the OG Verbal review and do it cover-to-cover.” Those aren’t bad resources, but WHY are you making a major study plan decision like that before you’ve really analyzed what’s up on a micro-level? Maybe you don’t need a full course, because the vast majority of your incorrect Verbal are in a specific area. Perhaps you think you’re super awful at RC, but when you go back through your three most recent CATs, you notice that it’s really just the RC Inference questions that you’re missing. Probably don’t need an entire RC book to get better at that one question-type! And you know what, maybe you DO need that course after all! But make a decision based on all the information, not out of confusion and panic.

  • The most common email I get is, “I’ve done 4,456,343 practice questions, and my score isn’t going up.” I’m serious. Okay, I may be exaggerating the number a tad. 😉 But I think the reason for this stagnation is that students just don’t know their weaknesses well enough. They just keep running on that hampster wheel.

  • The point of regular practice tests is to help you stop and take stock. It doesn’t matter that you scored a 450 on your last practice test. It doesn’t matter that you scored a 750 on your last practice test. The work is the same. A “score” that is churned out for you is not the true value of a CAT. Sure, it FEELS good to see improvement, but you need to go into the practice tests like a cold clinician (I know, easier said than done!).

I suggest that EVERYONE who is serious about improvement creates an Error Log spreadsheet to review every single incorrect Quant and Verbal question from the moment you start studying for the exam to the moment you finish you last practice question the night before your test (side note–please don’t do too much the night before your test!).
Will this be tedious? Yes.

Will this mean you will do fewer practice question? Definitely!

Is that a good thing? Abso-freaking-lutely!

And if you feel like you just can’t do it for every single practice problem, then you should AT LEAST be doing this for every single Official question you get incorrect, whether it’s from one of the Official Guides or from the GMATPrep practice tests.

In fact, I bet if you did this for every single practice question in the official guides, grouping all the similar questions together (doing all the CR Weaken first for example, then all the CR Evaluate, etc.), then carefully reviewing them once, twice, perhaps even three times, that might just be all the studying 80% of GMAT test-takers need.
Finally, remember that a GMAT course or a tutor is a gym membership.
It’s not liposuction.
But even outside the gym, you need to be thinking about HOW to use that gym, and deciding if you’re really making the kind of gains you want from the way you’re using that gym.
What a great opportunity right now during all this quarantine-time to take stock and make sure that the way you’re studying for the GMAT is the smartest, most efficient way of studying.
And if anyone would like an Error Log template for free, you can email me at gmatrockstar[at]gmail.com. No strings attached. You won’t be asked to sign up for tutoring with me, or put on a mailing list (I don’t even have a mailing list 🤣).

Here’s to getting your scores locked down in 2020 as efficiently as possible! 🙌

Tl;dr: Too often, students just throw money at courses and books hoping they will “do the trick” without doing the necessary self-analysis. DO THE SELF-ANALYSIS WITH AN ERROR LOG.

Social Distancing with Data Sufficiency Challenge! – Day 20

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This series is designed to help you step up your Data Sufficiency practice while we all spend a little extra time at home during the coronavirus situation; I’m going to publish one practice Data Sufficiency question each day! You can choose to do all of them, or none of them. 

Click on the tag “Social Distancing DS Challenge” at the bottom of this post to see all of the questions in this series! 

And remember to take whatever precautions you need to stay healthy over the next few weeks! 


Question #20

If x – y = z, what is the value of y?

(1) x = 7

(2) z = x + 4


 Explanation

Statement (1) is insufficient because, if we plug in x = 7 we are left with: 7 – y = z … and we still are unable to solve for y‘s value.

Let’s try plugging in statement (2): x – y = z … x – y = (x + 4) … -y = 4 … y = -4:  Statement (2) alone is sufficient! The correct answer is (B).

Social Distancing with Data Sufficiency Challenge! – Day 19

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This series is designed to help you step up your Data Sufficiency practice while we all spend a little extra time at home during the coronavirus situation; I’m going to publish one practice Data Sufficiency question each day! You can choose to do all of them, or none of them. 

Click on the tag “Social Distancing DS Challenge” at the bottom of this post to see all of the questions in this series! 

And remember to take whatever precautions you need to stay healthy over the next few weeks! 


Question #19

If j and k are integers, is j + k an odd integer?

(1) j > 12

(2) j = k – 1


Explanation

This is a pretty straightforward number properties question drilling us on our odds and evens rules. Remember that when adding, the only way to end up with an odd sum is to have an odd number of odd values in the list of numbers to be added together. If this is unclear, pick a few different values– odds and evens– and test it out! 🙂

Statement (1) doesn’t give us much to work with. It’s certainly not sufficient.
Statement (2) is enough to know for certain that the sum of j and k would be odd. Make up a few numbers to check it out. You’ll find that the sum of consecutive integers is always odd. Sufficient. The correct answer is (B).

Best Strategies for Tough GMAT RC Passages

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Today I want to look at a fantastically devilish RC question sent to me by one of my students yesterday (shout out, Vito!). It’s from the Official Guide Advanced book published last year.

If you don’t know about it, this book contains 8 really challenging passages that are worth going over in microscopic detail if you’re looking to build your RC skills up. The passages can be found on GMATClub (for free!). Just click the link above and copy/paste the beginning of each passage into Google to find the problem on GMATClub.

I want to look at the passage first. Don’t read it yet. Just skim your eyes over it as you scroll down…

⠀⠀⠀⠀⠀⠀⠀⠀Is there a massive black hole at the center of our
⠀⠀⠀ galaxy, the Milky Way? The evidence is inconclusive.
(5)  Just as the Sun’s mass can be determined, given
⠀⠀⠀ knowledge of other variables, by the velocity at
⠀⠀⠀ which its planets orbit, the mass at the center of the
⠀⠀⠀ Milky Way can be revealed by the velocities of stars
⠀⠀⠀ and gas orbiting the galactic center. This dynamical
(10)  evidence, based on recently confirmed assumptions
⠀⠀⠀ about the stars’ velocities, argues for an extremely
⠀⠀⠀ compact object with a mass two to three million
⠀⠀⠀ times the mass of our Sun. Although according to
⠀⠀⠀ current theory this makes the mass at the center
(15)  of the galaxy too dense to be anything but a black
⠀⠀⠀ hole, the relative lack of energy radiating from the
⠀⠀⠀ galactic center presents a serious problem. A black
⠀⠀⠀ hole’s gravity attracts surrounding matter, which
⠀⠀⠀ swirls around the black hole, emitting some energy
(20)  as it is engulfed. Scientists believe that the amount of
⠀⠀⠀ energy that escapes the black hole should be about
⠀⠀⠀ 10 percent of the matter’s rest energy (the energy
⠀⠀⠀ equivalent of its mass according to the equation
⠀⠀⠀ E=mc^2). But when the energy coming from the
(25)  galactic center is compared to widely held predictions
⠀⠀⠀ based on how much matter should be falling into a
⠀⠀⠀ theoretical central black hole, there is a discrepancy
⠀⠀⠀ by a factor of a few thousand.

Why is this passage hard?

  • It’s about Science. Many students will think, “ugh, I don’t know anything about Science!” Remember, you don’t have to know anything about the topic to get all the questions correct!

  • It’s all one long wall of text. It’s not very nice of them not to give us paragraphs, so we will have to subdivide the passage ourselves into manageable chunks as we read it. Look for transition words that seem like natural breaks.

Before we proceed, you might want to look at my Reddit post on Mastering RC Main Idea Questions to understand my theory on the three types of RC passages:

  • Informational

  • Informational + some opinion

  • Persuasive

Our categorization of the passage depends on how many keywords are present that indicate the author’s emotion/opinion.

Now let’s go through the passage.

I’m going to bold and italicize any such keywords:

⠀⠀⠀⠀⠀⠀⠀⠀Is there a massive black hole at the center of our
⠀⠀⠀ galaxy, the Milky Way? The evidence is inconclusive.
(5)  Just as the Sun’s mass can be determined, given
⠀⠀⠀ knowledge of other variables, by the velocity at
⠀⠀⠀ which its planets orbit, the mass at the center of the
⠀⠀⠀ Milky Way can be revealed by the velocities of stars
⠀⠀⠀ and gas orbiting the galactic center. This dynamical
(10)  evidence, based on recently confirmed assumptions
⠀⠀⠀ about the stars’ velocities, argues for an extremely
⠀⠀⠀ compact object with a mass two to three million
⠀⠀⠀ times the mass of our Sun. Although according to
⠀⠀⠀ current theory this makes the mass at the center
(15)  of the galaxy too dense to be anything but a black
⠀⠀⠀ hole, the relative lack of energy radiating from the
⠀⠀⠀ galactic center presents a serious problem. A black
⠀⠀⠀ hole’s gravity attracts surrounding matter, which
⠀⠀⠀ swirls around the black hole, emitting some energy
(20)  as it is engulfed. Scientists believe that the amount of
⠀⠀⠀ energy that escapes the black hole should be about
⠀⠀⠀ 10 percent of the matter’s rest energy (the energy
⠀⠀⠀ equivalent of its mass according to the equation
⠀⠀⠀ E=mc^2). But when the energy coming from the
(25)  galactic center is compared to widely held predictions
⠀⠀⠀ based on how much matter should be falling into a
⠀⠀⠀ theoretical central black hole, there is a discrepancy
⠀⠀⠀ by a factor of a few thousand.

There’s not much opinion here! The author only gives us two places where he personally weighs in. I ignored the word “believe” because that is associated with the “Scientists” and not our author.

Our author says that it’s “inconclusive” as to whether there’s a black hole, and he says that there’s a “serious problem” with the theory.

Remember — you don’t have to understand all the details as you read the passage!

Things We Don’t Need to Know Right Now:

  • what a black hole is

  • what a galactic center is

  • what “velocities” means

  • what E = mc^2 means

  • what EXACTLY the theory is

  • etc.

There are SO MANY details in this passage!!

If we carefully pored over each and every sentence and tried to “teach” ourselves exactly what it was saying, it would take us 8-10 minutes to read this passage.

(I’m not going to do the entire Passage Map for this passage, by the way, but if you’re curious what my notes would look like for my RC passages in general, you can check out this blog post on GMAT RC strategy.)

Takeaway #1 — The harder the passage, the LESS you should be focusing/stressing out on the details.

Let’s say you have 4 questions per passage on average (and in fact, that’s the number associated with this passage). One of those questions is very likely to be Main Idea. The other three are probably going to be Detail and Inference (occasionally they throw in a Function question).

That means for this ENTIRE passage, there are only THREE questions for which you will need to go back to the passage and actually locate and understand a detail.

Why should we spend our time understanding every single sentence up front, when we’ll have to go back and re-read anyway later on, and there might only be 3 sentences we need to comprehend, anyway?

Now, since we know there’s three types of passages, we can see that with only TWO pieces of opinion, this is not going to be classified as a Persuasive passage.

And since there is some opinion, it can’t be purely Informational.

So we will classify this as an “Informational + some opinion” passage.

Now let’s take a look at the challenging question. Set a timer for 2 minutes and give it a shot!

The “serious problem” referred to in line 17 could be solved if which of the following were true?

A. Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high.
B. Current assumptions about how much matter a black hole would engulf proved to be a few thousand times too low.
C. The object at the center of the Milky Way turned out to be far more dense than it is currently estimated to be.
D. The object at the center of the Milky Way turned out to be far more massive than it is currently estimated to be.
E. Matter being engulfed by a black hole radiated far more energy than is currently assumed.

Now let’s break it down:

Takeaway #2 — Always rephrase the question in simpler terms!

REPHRASE: What would solve the “problem”?

We have two tasks here:

  • figure out what the heck the “serious problem” is

  • figure out how to solve it

Most people will probably not try to brainstorm how to solve whatever this “serious problem” is, and I think that’s the key here. We need to answer the question posed on our own first before looking at the answer choices!

What makes this question easier is the fact that we already noticed the phrase “serious problem” as we read the passage, because it was one of the few places the author had an opinion!

Takeaway #3 — There will almost always be an Inference question asking about the Author’s Opinion.

They were nice enough to give us the line number for this question, but we didn’t need it!

“Although according to current theory this makes the mass at the center of the galaxy too dense to be anything but a black hole, the relative lack of energy radiating from the galactic center presents a serious problem*. A black hole’s gravity attracts surrounding matter…”*

Another place where a mistake could be made, strategically, is in stopping here and not continuing to scan down for anything else that describes the “problem.” There’s a bit more towards the end of the passage that elaborates:

“But when the energy coming from the galactic center is compared to widely held predictions based on how much matter should be falling into a theoretical central black hole, there is a discrepancy by a factor of a few thousand.”

To synthesize: “Serious problem” is the lack of energy in the galactic center (and there’s a discrepancy with predictions)

So, what would solve this problem?

Either the “widely held predictions” are wrong and it’s a black hole even though it falls short by a few thousand, or perhaps the measurement itself is inaccurate and there’s more energy than they thought?

PREDICTION: Measurement of Milky Way wrong or No Discrepancy.

Takeaway #4 — Always WRITE DOWN an answer in your own words before reading the answer choices!!!

Back to the answer choices:

A — this matches the 2nd part of our prediction  (shows no discrepancy, the low energy isn’t really “low” after all!)
B — this is opposite of A so it’s wrong
C — Density has nothing to do with our prediction
D — Mass has nothing to do with out prediction
E — Similar to A

A and E are clearly the final two, and this is where most people will give up under the weight of the science mumbo-jumbo.

The difference is that (A) is really doing the job we need here — the job of FIXING this “problem” — it’s more specific to the situation at hand.

Just because (E) is true, it doesn’t indicate that this would be a black hole necessarily. It’s just giving a trusim about “matter.” Just because when MATTER is engulfed it radiates more energy in general doesn’t help fix our discrepancy, because what if it’s just not a black hole in this case? Then (E) wouldn’t even apply at all. Whereas (A) is saying we’re getting something wrong about black holes! Not just matter.

Takeaway #5 — Prove to yourself why the 2nd best answer is 2nd best!

Notice we didn’t just pick (A) because it came first. We took our time, recognized that this was going to be a deathmatch between (A) and (E) and then we kept at it until we understood the difference between the Correct Answer and the 2nd Best Choice.

But, Vivian, won’t this take me more than 2 minutes???

A few thoughts on RC and timing:

  • Get “good” before you get “fast.” — I don’t care if it takes you 30 minutes per passage in the beginning. Work hard on your strategy. Spend time breaking down passages. Spend time rephrasing question-stems. Spend time breaking down answer choices.

  • Go through all the RC Official Guide passages at least twice. Make sure you understand all the pitfalls associated with the passage, question-stems, and answer choices. Don’t just “do them” and check a box. Absorb them! For help on how to do this, check out my post on How to Review Official Guide RC Questions a Second (or Third!) Time

  • When your RC accuracy is 90% untimed, you can start to time yourself. Otherwise, you haven’t earned it, and your strategy still isn’t good enough. Consider booking a few sessions with a tutor if you need to walk through RC with someone who knows what they’re doing.

  • You can skip a hard RC question on the Exam. It’s not a big deal! 🙂 If you see a question like the one above and you know it might take you 3+ minutes, you can 100% “opt out” of the question, and in most cases it will probably be the smartest decision you could make! There is no rule that says you have to answer all the questions just because you read the passage. I promise no one will know if you only attempt 3/4, and you’ll feel good that you skipped one you knew you wouldn’t get right. So, as you do those RC OG passages, imagine you’re seeing them on Test Day. What questions just wouldn’t be worth your time? 🙂

Finally, I just want to say, DON’T GIVE UP. You are not stupid.

Passages are hard. Questions are hard. The GMAT is hard!

Keep at it. This is a teachable skill and a learnable skill! 🙂

Social Distancing with Data Sufficiency Challenge! – Day 18

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This series is designed to help you step up your Data Sufficiency practice while we all spend a little extra time at home during the coronavirus situation; I’m going to publish one practice Data Sufficiency question each day! You can choose to do all of them, or none of them. 

Click on the tag “Social Distancing DS Challenge” at the bottom of this post to see all of the questions in this series! 

And remember to take whatever precautions you need to stay healthy over the next few weeks! 


Question #18

Is the number x between .5 and .9 ?

(1) 800x < 620

(2) 1200x > 620


Explanation

Let’s solve for x in each inequality statement.

Statement (1): 800x < 620 … x < .775  … That alone is not sufficient to say that x is in the presented range, since we can’t be sure x isn’t less than .5
Note: The easier way to think about this without using a calculator is to think about fractions and decimals you know well. Reduce this fraction first by ten (80x < 62), then cut it in half (40x < 31), and finally isolate the x: x < 31/40.  What’s really close to 31/40 that you know well? Let’s use 3/4, which equals .75.

Statement (2) = 1200x > 620 … x > .517 … Statement (2) is also not sufficient alone.
Suggestion: Handle this calculation the same way as you did statement (1). 1200x > 620 … reduce by ten: 120x > 62 … cut in half: 60x > 31 … isolate x: x > 31/60 which is just barely more than .5 … no lengthy calculation needed!

But combined with statement (1), we know that x is in the range: .517 < x < .775, which is within the range presented of .5 < x < .9

The correct answer is (C).

Social Distancing with Data Sufficiency Challenge! – Day 17

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This series is designed to help you step up your Data Sufficiency practice while we all spend a little extra time at home during the coronavirus situation; I’m going to publish one practice Data Sufficiency question each day! You can choose to do all of them, or none of them. 

Click on the tag “Social Distancing DS Challenge” at the bottom of this post to see all of the questions in this series! 

And remember to take whatever precautions you need to stay healthy over the next few weeks! 


Question #17

Is x a positive number?

(1) 8x > 7x

(2) x – 2 is negative.


Explanation

Statement (1) is sufficient, since that inequality would only hold true for a positive value of x. Make up some numbers to test it out. We know statement (2) is not sufficient because there are both positive and negative values of x that satisfy the statement “x – 2 is negative.” The correct answer is (A).