Earthquakes occur when energy in the earth’s crust is sudden

[I_need_a_700plus]

The following problem was in the IR section of the CAT exam.

My question is, if the answers A, B, C, D are all incorrect, doesn't that mean they qualify as "false"? If yes, then how would you distinguish with "false" answer is the right answer?

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Earthquakes occur when energy in the earth’s crust is suddenly released, forcing tectonic plates to shift. Earthquakes are classified as foreshocks, main shocks, or aftershocks. What differentiates one category from another is their relation to each other in space and time. A foreshock is only a foreshock if it occurs before a bigger quake on the same fault system. Similarly, an aftershock occurs only after a bigger quake on the same fault system. Interestingly, the probability that an earthquake will trigger a bigger earthquake does not depend on the magnitude of the first earthquake, but rather is related to the location of that first quake and its interaction with the fault system.

In the first column, indicate the statement that the given information most strongly suggests is true. In the second column, indicate the statement that the given information most strongly suggests is false. Make only two selections, one in each column.

A - All main shocks are preceded by foreshocks.
B - All main shocks are followed by aftershocks.
C - Aftershocks are more common that foreshocks.
D - Foreshocks are generally weaker than aftershocks.
E - Main shocks can be triggered by foreshocks.
F - An aftershock can be a bigger earthquake than the main shock that preceded it.

[RonPurewal]

so, basically, there are three situations you could have with each choice:

1/ you know it's true
2/ you know it's false
3/ you just don't know

given the directions to this problem, you know you're going to have one of #1, one of #2, and four of #3.

there are a lot of big words here. i prefer things that a nine-year-old would understand, so let's stop talking about earthquakes, and talk instead about animals walking in a line.
foreshock = fox
main shock = monkey
aftershock = armadillo

A foreshock is only a foreshock if it occurs before a bigger quake on the same fault system

--> if you see a fox, there will always be a monkey (which is bigger than a fox) right behind it.

an aftershock occurs only after a bigger quake on the same fault system.

--> whenever you see an armadillo, there will always be a monkey (which is bigger than an armadillo) right in front of it.

notice what we don't have here, which is anything definite about seeing a monkey.
you could just see a monkey, all by itself. or it could have an armadillo behind it. or it could have a monkey in front of it.


let's look at the 4 indeterminate statements.
note that these are neither necessarily correct nor necessarily incorrect; they're just indeterminate (i.e., you can't tell whether they are true or false).

1/
All monkeys have foxes in front of them.
--> We don't know anything about what's necessarily around a monkey.

2/
All monkeys have armadillos behind them.
--> We don't know anything about what's necessarily around a monkey.

3/
There are more armadillos than foxes.
--> ???
We have no information that pertains to this at all.

(Exercise for you: We can prove that there are at least as many monkeys as foxes, i.e., the number of main shocks is at least as great as the number of foreshocks. See if you know why.)

4/
Foxes are smaller than armadillos.
--> ???
We just know that both of these are smaller than monkeys, but there's no basis for a comparison between them.