Inferring from the Meteor Stream Passage
Last time, we took a look at the Meteor Stream passage from the free set of questions that comes with GMATPrep (not from the practice CATs). Click the link in the previous sentence and open up that passage in a separate window (I’m not going to show it here because it’s so long!).
Ready for the question? Give yourself about 1.5 to 2 minutes to answer.
The Question
The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in the highlighted text and the new computer derived theory?
[Note: when this question is given during the test, the phrase Conventional theories is also suddenly highlighted in yellow in the passage. This text appears at the start of the second-to-last sentence of the first paragraph.]
(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.
Solution
This is a detail question, so we’re going to use our notes and any clues in the question stem to know where to look. The question stem gives us one huge clue: it actually highlights a portion of a sentence in the first paragraph.
Next, the question says the passage suggests, so this is an inference question. Finally, the question is asking for a prediction that can be drawn from both the conventional theories and the new computer theory”in other words, where do these two theories agree?
Take a look at your notes. Mine are below, but everyone will have somewhat different notes.
| P1 | MS around cometsame orbit, diff velocmodel of G vs. theory |
| P2 | Earth + MS = showeractivity varies (?) |
| P3 | model = reality? Y. (?)G 3,000 yo |
Hmm. Well, the yellow highlighter already gives us a clue that we’ll need to use paragraph 1 and my notes reinforce that message: the model (or computer model) of the Geminid vs. the (conventional) theory. All right, back to paragraph 1 we go!
Paragraph 1
As a general rule, start a sentence or so before the cited text.
The reseNavigator found, as expected, that the computer-model stream broadened with time. Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.
Hmm. The first sentence says that as expected, the computer-model stream broadened with time. If this was expected, then both the computer model and the conventional theories must be in agreement on this issue. The next two sentences indicate a contrast: however and surprisingly. This information, then, can’t be where the two agree.
Glance through the answers. Argh! None of them specifically talk about how broad the stream is.
Oh, right, wait a second! This is an inference question. We can’t just spit back what the passage already says; we have to infer something. Okay, what else does the passage say about the stream broadening? Check a bit earlier and a bit later than the areas we’ve already read.
Earlier, the passage does confirm that astronomers hypothesized that the stream would broaden and the computer model tested that hypothesis. That info doesn’t tell us anything more to do with the size or breadth of the stream, though.
Later, in the first sentence of the second paragraph, the passage indicates that a meteor shower occurs whenever the Earth is passing through a meteor stream. Can we infer anything here? When the meteor streams are young, they’re more narrow; as they get older, they get broader. What effect would this have on the meteor showers that occur when the Earth passes through a meteor stream?
In general, the bigger and broader the stream, the longer it would take for the Earth to pass through it”so we would expect a much more interesting meteor shower (or, at the least, a longer one).
(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
This isn’t what we were just talking about, but I do feel like I read this somewhere check the passage. Yep! It’s in there, just before the bit about the conventional theories. The passage says that In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream, the Geminid. Hmm. That’s how they made the model, yes, but there’s no indication that the conventional theories also held to this, and we’re looking for something on which both things agreed.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
Most meteor streams? The universe is a pretty big place. It seems impossible that there would only be meteors right around our own little planet. The passage says only that when they do cross our path, we’ll see a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
The passage did say something about this yep, at the end of paragraph 1. This was the surprising result of the computer model; the conventional theories disagreed. This one’s definitely wrong.
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
Yes, this is pretty much what we said above: a bigger meteor stream would take longer to pass through, so the older ones would take longer.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.
The only thing I remember seeing about the individual particles was something about velocities at the beginning. The passage never mentions anything about their size.
The correct answer is (D).
We did have to get into the detail here, and that took some time. We didn’t read all that detail carefully on the first read-through, so here’s where we concentrate on several specific sentences and try to figure things out. On a question like this one, if at all possible, try to formulate at least an idea of what the answer must or might include before looking through the answer choices.
If you’re not sure, then first try to eliminate answers that are never mentioned in the passage at all. In this case, answer (E) mentions the size of dust particles, but that’s never mentioned in the passage.
Next, look for answers that don’t make common sense. Answer (B) doesn’t make sense because the Universe is enormous; it’s very unlikely that most meteors out there will cross our path at some point.
Finally, if you do pick up that the question is asking for agreement between the conventional theories and the computer model, then cross off answer (C), because the information in that choice is presented in the however and surprisingly sentences of paragraph 1.
Now you’re down to two choices; guess and move on.
If you can’t get enough of the Meteor Stream passage, check out our ensuing post here.
Key Takeaways for Inference Questions
(1) First, figure out where to look; the clues will be in the wording of the question itself. In this case, they highlighted a couple of words for us, but they also gave important direction when they asked what could be derived from both the theory and the model.
(2) Whenever possible, know what you’re not looking for as well. In this case, the question asks where the theory and the model agree, not where they disagree. Because the passage does also give info about where the two contradict, chances are a trap answer will include that info.
(3) If the text is just too hard to understand, use a couple of tactics to try to eliminate some wrong answers. Anything that isn’t actually mentioned in the passage can be crossed off. You can also use common sense; if something really doesn’t make sense in the real world, don’t guess that one.
* GMATPrep text courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.