If a mother's first child is born before its due date, it is likely that her second child will be also. Jackie's seco...

Ilana on May 11, 2020

Why isn't B the correct answer?

I am confused because the argument in the question stem is reversing and that is exactly what B is doing as well. How can C be the answer when it is a valid argument like the rest of the choice options?

Reply

Shunhe on May 12, 2020

Hi @izyat,

Thanks for the question! So you’ve correctly identified that the question type here is going to be parallel reasoning. Let’s take a look at the stimulus, which I’ll diagram. The first sentence can be diagrammed as follows:

First child born before due date = FCBE (E standing for early)
Likely that second child also born before due date = LSCBE (E standing for early)

FCBE —> LSCBE

Now we’re told that Jackie’s second child wasn’t born before its due date, so it’s likely that the first one won’t be born before either. In other words:

SCBE = second child born early
LFCBE = likely that first child born early

~SCBE
Therefore: Likely ~FCBE

Now, notice here that what’s going to be important is the misusage of “likely” here. We can’t really use probabilities in the way that the argument is using them. To diagram the stimulus in an abstract way:

A —> Likely B
~B
Therefore: Likely ~A

So we need something that matches this reasoning. Let’s take a look at (C). We’re told in (C) that if a movie is a box-office hit, its sequel will likely be also. Hawkman II wasn’t a box-office hit, so Hawkman I probably (likely) wasn’t either. Diagramming this, we get:

Movie box-office hit —> Likely sequel box-office hit
~Sequel box-office hit
Therefore: Likely ~Movie box-office hit

And if we replace “movie box-office hit” with A and “sequel box-office hit” with B, we see that we get the same reasoning structure:

A —> Likely B
~B
Therefore: Likely ~A

And so (C) is the correct answer.

(B), on the other hand, is different reasoning. Diagramming (B), we get

Responsible pet owner —> Likely good with children
Good with children —> Likely responsible pet owner

But this misses out on the fact that the terms were both reversed and negated, which (C) captures, and this is why (B) is wrong.

Hope this helps! Feel free to ask any other questions that you might have.