Logical reasoning PrepTest 138 · Section 3 · Question 9

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Laundry detergent → Surfactants, which hurt aquatic life
The environmental effects of other ingredients are unknown
Therefore - No reason to believe ecologically friendly detergents are better for the environment

Answer Anticipation:
For most argument-based questions, starting with the conclusion and thinking about what would need to be established to prove it can be a great way to set the stage for analyzing how the premises fall short.

Here, the conclusion is very extreme—there's "no reason" to prefer ecologically friendly detergents to protect the environment. If there's a single, minor reason to prefer them—some small way they're better for the environment than others—this argument is undercut.

Do the premises leave open the possibility that there is a reason to use them? It does establish that all detergents—including the environmentally friendly ones—have surfactants, which damage aquatic life. And it establishes that all other ingredients have unknown impacts on the environment. So the ingredients in the detergents seem to be a wash—there really is no reason to go with ecologically friendly detergents over other ones based on the ingredients.

But we have to weaken this argument, so there must be something different about them that would point to the ecologically friendly detergents being better for the environment. If this is as far as you reached in your anticipation, there's nothing wrong with that—heading into the answers looking for a relevant difference between the detergents would be sufficient in finding the correct answer.

Taking it a step further, if it's not the ingredients included in the detergents, then it must be how much of the damaging ingredients are in them. While all detergents contain damaging surfactants, if the environmentally friendly ones contain significantly less of them, then it could be more environmentally friendly, thus undercutting the argument.

Answer Explanation:
This answer highlights a relevant difference between ecologically friendly detergents and the others—they have lower levels of damaging surfactants. If that's the case, then there's reason to believe that they are less damaging to the environment, undercutting the argument that there's no reason to believe that.

Key Takeaway:
In an argument that reaches a comparative conclusion, relevant similarities and differences are generally correct answers. Figuring out which you're looking for can be enough of an anticipation to get to the right answer accurately and efficiently!

Incorrect. This answer would bring up a relevant similarity between all the various detergents, thus reinforcing the conclusion that they're all about the same.

Incorrect. Without tying the more damaging surfactants to the non-ecologically friendly detergents, this answer doesn't undercut the conclusion.

Incorrect. Without tying these ingredients to the normal or ecologically friendly detergents, there's no way to assess the effect this has on the argument.

Incorrect. Needing to use more would align with the argument—it can't be the case that that would be better for the environment.