Logical reasoning PrepTest 125 · Section 2 · Question 26

Incorrect. First, this answer is a reversal of one of the conditional premises. Second, it adds in causality ("because") which, while strongly suggested by the stimulus, is never directly stated.

Incorrect. When we were reading through the stimulus and saw that one premise was based on what the newspaper claimed, we started to think that the argument might be assuming the newspaper was correct. However, since the conclusion is conditioned on the newspaper being correct ("So, if the newspaper is correct . . . "), so it's not assuming it's right.

Incorrect. Even if they were the only company in the area selling those parts, that doesn't guarantee the parts are hard to find. Again, there might be a store one town over, or an online retailer that sells the parts openly.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen with Sufficient Premise

Stimulus Summary:
Parts for old sirens hard to find → Government buys and installs new weather sirens
Newspaper: New sirens installed → Public safety enhanced
Local store that sold those parts is out of business
Therefore - Newspaper correct → Public safety enhanced

Answer Anticipation:
An interesting stimulus! It's heavily based on conditional logic, but there are a few gaps that we'll need to address. Some are logically allowed, but one of them will represent a true gap in the argument that will show up as the correct answer.

Let's start with the conclusion and work backwards:
Newspaper correct → ??? → Public safety enhanced

Looking at the "endpoints" in the conclusion, we can see that both are present in the premises, so we'll need to find a gap between them instead of between the premises and conclusion. Starting with the sufficient condition, if the newspaper is correct, then the new sirens will guaranteed public safety is enhanced:
Newspaper correct → (New sirens installed → Public safety enhanced)

Doesn't that guarantee the necessary condition follows? Nope! While the newspaper being correct establishes a sufficient condition for determining public safety is enhanced, it doesn't establish that that condition is met. So now, to reach the conclusion, we're looking to establish that the new sirens are installed.

What will guarantee that happens? The first conditional tells us—if parts for the old sirens are hard to find, then the government will buy and install new weather sirens. So we've now branched out a bit from a straightforward chain, but that's fine, because working backwards we're still making progress! To reach the conclusion, therefore, it needs to be established that parts for the old sirens are hard to find.

Does the argument do that? Nope. Instead, it says that the place where those parts were purchased last year is now out of business. While that might make it harder to find the parts, it doesn't guarantee they'll be hard to find—maybe there's a store the next town over, or an online retailer that could be used.

The correct answer, therefore, will either directly establish that the parts for the old sirens are hard to find or, more likely, connect the store going out of business to the parts being hard to find (since Strengthen with Sufficient Premise questions generally don't provide extraneous information).

Answer Explanation:
This answer establishes that if the old company is out of business, the parts for the old sirens will be hard to find. That guarantees the government will buy/install new sirens, which (if the newspaper is right) will increase public safety. If added to the argument, this answer allows the conclusion to follow logically from the premises, so it's the correct answer.

Key Takeaway:
For Strengthen with Sufficient Premise questions that have particularly complex arguments, it can be helpful to "build backwards" from the conclusion to find the gap.

Incorrect. The quality or reliability of the parts are out of scope. The condition that guarantees new sirens will be installed is that the parts are hard to find, not quality parts.