PrepTest 154, Section 4, Question 21
Engineer: Air bags in automobiles occasionally cause injuries(63 more words not shown)
The engineer's argument is most(10 more words not shown)
- AIt fails to(24 more words not shown)
- BIt takes for(19 more words not shown)
- CIt fails to(20 more words not shown)
- DIt overlooks the(25 more words not shown)
- EIt overlooks the(23 more words not shown)
Reading the argument
More ways to fail doesn't necessarily mean more failures.
An air bag going off without a collision sounds like a real problem. That doesn't mean air bags are a bad idea overall; preventing injuries in crashes could still make them valuable. But the engineer's conclusion concerns a narrower question: whether new control systems will make accidental inflation worse.
I can understand being cautious about a more elaborate computer system. Adding complexity can introduce new things that might go wrong. Still, how often will those things happen compared with the failures the new system prevents?
Imagine the old system failing 20 percent of the time and the replacement failing only 1 percent of the time. Those are hypothetical numbers, not air bag statistics. Even if the replacement has more possible failure modes, it would be far more reliable in that example. It could fix common old failures while introducing several much rarer possibilities.
What we’re looking for
For the flaw question, that's the comparison we need. Counting possible problems doesn't tell us their overall likelihood. The engineer needs evidence that the new system actually produces more accidental inflation, not just that we can list more ways something could go wrong.
Working the answers
- ACorrect
This captures the distinction between the number of ways a system could fail and the chance that it actually will fail. A thousand extremely unlikely failure modes needn't be worse than a few common ones.
Our example comparing 20 percent with 1 percent makes the gap concrete: complexity could increase while failures decrease. The engineer moves from more possible failure routes to a prediction of worse accidental inflation without establishing the likelihood needed for that prediction.
- B
The argument needn't assume that every control-system failure makes the air bag inflate. It could allow some failures to have other effects and still predict more accidental inflation. The stronger objection is that adding possible failure modes doesn't establish a higher overall failure rate in the first place. B's claim about every failure goes beyond what the reasoning requires.
- C
Accidental inflation from some other cause is possible, but that alone doesn't show what adding these control systems would do to the problem. Other causes could remain while the new system either improves or worsens matters. Don't read the first sentence as proving that computers aren't involved; it doesn't identify the existing cause. C doesn't address the missing comparison of failure likelihoods.
- D
This grants the precise conclusion we're challenging: the new systems make accidental inflation worse. Perhaps they also offer other advantages, such as lower costs. That could matter to a broader decision about using them, but it wouldn't undermine the narrower claim about accidental inflation. The engineer hasn't concluded that the systems have no benefits of any kind.
- E
This returns to our initial thought that air bags could still be worthwhile overall. An air bag might prevent more injuries than it causes while a particular new control system worsens accidental inflation. Both could be true. E evaluates air bags overall, rather than the engineer's prediction about the proposed control systems.
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