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Inference Questions

Mike McGarry
Lesson by Mike McGarry
Magoosh Expert
Learn More About Magoosh GMAT
Now, we'll talk about inference questions. Many GMAT reading comp questions ask about what patches clearly and explicitly states. Inference questions asked for what is not explicitly stated, but implied with near certainty. In other words, given what the author did say, what conclusion is unavoidably obvious?

That's what we're looking for in an inference question. So we want something that has to be true even though it's not set. Here is a simple argument. So which of the following has to be true? Pause the video and look at this for a minute, then we'll talk about it. Okay, in a class of 20 students, 19 passed the class and only Leonard failed.

In terms of the GMAT's standards, what can we include? One, A, Leonard is not the brightest student in the class. Well, what if he is the brightest student in the class? What if he some kind of super bright Einstein character, but he just got bored with the class and didn't do any work and that's why he failed. So that is one possible explanation.

So it's not necessarily true that Leonard is not the brightest student in the class, so we eliminate that. Leonard did not learn the material in the class. Well, again, Leonard might have learned all of it. But for whatever reason, maybe he was sick during the final exam and was not excused or decided to blow off the final exam for personal reasons or whatever even though he knew all of the material inside out.

So that certainly could be true also. So we can't say that B is a good inference. C, Leonard did not work as hard as all of the other students. Maybe he worked twice as hard. And so this might be maybe he didn't have the ability. He worked ten times harder, but he just couldn't get there, because he wasn't bright enough to understand it.

That also could be a way that it played out. And so we can't conclude C either. So A, B and C, in fact, none of these would qualify at GMAT inferences. If it's anything where gee, it could be true or we could imagine that it's not true, that is not an inference. An inference absolutely has to be true.

So the forms of this question stem, several different forms. The passage implies that, which of the following can be inferred? The author would probably agree with which of the following. The passage suggests that X would be most likely to agree with blah, blah, blah. So many different forms of this question type. All of these question types stem from possibility and uncertainty, because the inference isn't stated literally in black and white.

Nevertheless, a good GMAT inference is just a hair's breadth away from what is explicitly stated. In other words, if everything explicitly stated is true, then there's no way that the inference could not be true. An inference is an additional unstated fact that absolutely must be true, given all that was stated.

The distractors on inference statements would be those statements that could be true, even that are relevantly likely to be true, but which aren't guaranteed to be true. A good distractor might be one that at first appear looks like it might always be true. But when we think more carefully, we realize it doesn't actually have to be true.

Here's a very simple, not-very-GMAT-like example. Pause the video and then we'll talk about this a little bit more. Okay, thieves were able to enter the bank at night without activating the alarm. They began to hand bags of money through a small window for an accomplice to load in a van. After half an hour, when they're almost done, someone accidentally knocked over a coat rack and the sound triggered the alarm.

All the thieves immediately ran to the van and departed with the cash they had, escaping from the scene just before the police arrived. What can we infer from this passage? So here are possible inferences. Pause the video again and decide for yourself which one of these would be valid inferences, and which one would not be valid inferences?

Okay, these were able to avoid arrest for this robbery. All we know is that they got away just before the police got there, but we don't know when they got away. Maybe was there some way that their car was photoed or something like that. We have no idea. And maybe later in that day, they were caught red handed with all of this cash.

We have no idea. So maybe they were able to avoid arrest, but we don't know that. So we eliminate that one. This bank was relatively easy to rob. We don't really know about this. All we know is that these people managed to rob it.

How much technical skills that they need to pull off this robbery? Were they able to pull off something that no one else had been able to pull off? We don't know. So we don't know that it was relatively easy to rob, so we eliminate that. The bank customers lost a lot of money. We don't know this.

In other words, in fact, it's likely in the United States that the money was FDIC insured. And so probably the bank lost money, but the customers didn't actually lose money. And so it does seem like this is something that we don't know would be true. The bank's alarm made a loud sound. That's interesting.

Do we know that the alarm was a sound? We know that the thieves were aware that the alarm had been triggered, but was it a sound or was it silent flashing lights or was it just a red light on a certain screen or a certain buzzer and they recognize it? We don't really know. So might have been a loud sound or maybe it wasn't a loud sound.

We don't know that. The thieves had some way of knowing whether the alarm was on or off. Okay, now this one has to be true. Because the thieves left as soon as the alarm went on, because they changed their plan and left. They must have realized that the alarm was on, that the alarm had been set off.

And so if they realized that the alarm had been set off, they had to have some way. Now we don't know whether it was a sound or a light, or some kind of electronics single. We don't know what it was, but somehow they have a way of knowing that the alarm came on. And so they knew this.

And so that something we can refer. The bank's alarm was triggered only by a loud sounds. We don't know this. Was it also triggered by some kinds of movement? Now obviously, it wasn't triggered by everything they were doing, but were there other things that could trigger the alarm?

Maybe coming in the front door, maybe movement in the main space in the back. We have no idea what might or might not trigger the alarm and we don't know that it was triggered only by loud sounds. We don't even know whether the coat rack falling over was a particularly loud sound. All we know is that it did make a sound, but we don't know.

So we can't conclude that. Handing bags of money out that small window did not activate the alarm. Well, this is something we do know, because they spent a long time handing bags of money out that window. They're spending a long time doing that and the alarm didn't go off, so it just mean that doing that did not trigger the alarm.

So that is a valid inference. And then finally, the police station was relatively far away from the bank. All we know is that the bank robbers left and then the police arrived soon after they left. We don't know how far away it was. We have no idea how far away it was and we also don't know the cars that came.

Did they come directly from the police station or were they out patrolling and they came from wherever they were on patrol? There's a lot we don't know about that, so we can't infer that. The first important point to keep in mind about GMAT inferences is that while unstated, a good inference has to be true. It's also generally true that the gist of an inference will be consistent with the author's main point and is unlike to contradict the main point.

Here's the passage. Pause the video and then we'll talk about this. Now, we'll look at the answer choices again. Pause the video, study these and see if you can identify the inference. Okay, now we can talk about this all. Dark matter and dark energy have little effect on conventional matter over familiar distances.

Instead, they make their presence known through their prodigious gravitational effects. In tracking them down, therefore, astronomers have had to study gigantic assemblages of matter, extending across spans of millions and even billions of light-years. Perhaps the first to take that sweeping viewpoint was this guy Fritz Zwicky.

In 1930s, Zwicky traced the motion of individual galaxies within great clusters of galaxies and made the remarkable discoveries. The individual galaxies are moving too fast to be held together in a cluster by the force of gravity exerted by the starry matter within them. From his measurements, Zwicky concluded that the great clusters must be held together by the gravitational effects of some unseen mass which he dubbed dark matter.

And so that's a very complicated passage and it can be inferred from the passage that Zwicky hypothesized the existence of dark matter in order to account for what? One, the speed that in which the galaxies are moving away from one another. Well, no, not so much. It's not so much that they have that speed, but it's why can they move at that speed?

Are they still being held together, even when they're moving at that speed? That's the thing that really was explained. So A is not correct. B, the manner in which large galaxies tend to clump together. Well, in fact, what's happening is the galaxies are moving apart. But the way they're moving, we don't understand why they're still held together even though they're moving apart.

And so B is not correct. C, the great, the distance between certain galaxies. This is out of scope not true at all. D, a phenomenon in which visible matter alone is unable to explain. So in other words, there was something that could not be explained, but the visible matter.

And so we have deposit something be on the visible matter. And so this is actually something quite true and quite close to what the passages actually say. E, the behavior of galaxies outside of great clusters, that is outside of scope. He's only talking about galaxies within the cluster. And so the best answer here Is answer choice D.

In summary, on the GMAT, an inference, while stated is a fact that must be true, based on what is stated. Distractors will be statements that could be true, that might seem to be quite plausible, but they don't have to be true. In most cases, a good inference will be aligned with the author's main purpose.

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Reading Comprehension