In 1990 major engine repairs were performed on 10 percent of the cars that had been built by the National Motor Compa...

Ravi August 12, 2019

@Julie-V,

Happy to help.

In the stimulus, we have two groups of cars. The first group is cars
manufactured in the 1970s, and the second is cars manufactured in the
1960s. 10% of the of the 1970s cars received repairs, but only 5% of
the 1960s cars received repairs. This is odd, as one would expect that
older cars would have more repairs performed on them. This is the
discrepancy in the stimulus.

That said, there's a really important factor that isn't addressed, and
that is the number of the 1960s cars that actually need repairs but
don't end up getting them. Maybe some of these 1960s cars are still
registered but are just collecting dust in people's garages, so even
though they technically need to be repaired, they're not getting
repaired. Alternatively, maybe the older cars aren't getting repaired
as much because it's not worth repairing them.

We're looking for the answer choice that most helps to explain the discrepancy.

(A) says, "Government motor vehicle regulations generally require all
cars, whether old or new, to be inspected for emission levels prior to
registration."

The problem with (A) is that we don't know whether the cars in
question were already registered (and therefore would not need to be
inspected for emission levels under this law), so (A) doesn't apply to
the conditions laid out in the stimulus. Thus, we can get rid of this
answer choice.

(B) says, "Owners of new cars tend to drive their cars more carefully
than do owners of old cars."

None of the cars described in the stimulus were new at the time of the
study, nor are we entirely sure how driving a car carefully affects
the repairs needed, so this answer choice doesn't change the stimulus.
Thus, (B) is out.

(C) says, "The older a car is, the more likely it is to be discarded
for scrap rather than repaired when major engine work is needed to
keep the car in operation."

(C) looks great, as it tells us something that the stimulus does not
mention. Although fewer repairs were performed on the older cars, this
does not mean that they needed fewer repairs. If the cars are being
discarded for scrap instead of being repaired, then this explains the
higher incidence of repairs among the newer cars, so (C) is the
correct answer choice.

(D) says, "The cars that the National Motor Company built in the 1970s
incorporated simplified engine designs that made the engines less
complicated than those of earlier models."

If the engines in the newer cars are less complicated, it would seem
that they should be having fewer repairs than the older cars rather
than more. If anything, this deepens the paradox, so (D) is definitely
incorrect.

(E) says, "Many of the repairs that were performed on the cars that
the National Motor Company built in the 1960s could have been avoided
if periodic routine maintenance had been performed."

Knowing that some of the repairs could have been avoided doesn't
explain why the older cars received fewer repairs than the newer cars.
Plus, if anything (E) makes it seem like the older cars should have
even fewer repairs, to this would only deepen the paradox. Thus, (E)
is out.

Does this make sense? Let us know if you have any other questions!

rinavaleriano May 2, 2021

I got this wrong but I narrowed it down between C & D. I thought D makes sense because the engine being more simple doesn't nec. mean it should break down less than the older ones? I thought that if the engine is more simple, then it may make it easier to repair. Hence, they repair more of the engines that are easier.