Logical reasoning PrepTest 127 · Section 3 · Question 13

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Tent caterpillars leave behind chemicals. The trails to food sources are heavier than exploratory routes. Therefore, the tent caterpillars leave the trails to communicate where food is.

Answer Anticipation:
The argument here compares two types of chemical trails—the heavier ones that lead to food, and the lighter ones that don't lead to food. From this, the argument concludes that these trails convey information to caterpillars—they tell the bugs how to get to food.

However, there's a big assumption in there—that the caterpillars, when looking for food, follow the heavier trails. There's no suggestion that this is the case, and so the argument is flawed. To strengthen this argument, then, we should establish that the comparison raised—how heavy the routes are marked—is relevant to the conclusion about how food is found.

Answer Explanation:
This answer makes the comparison raised about how heavily marked the routes are relevant to the conclusion about these trails communicating information about where food is. It therefore strengthens the argument.

Key Takeaway:
Whenever there's comparative logic in the stimulus of an argument, analyze that comparison to see if it is used in a valid manner. Here, the comparison was never established as relevant to the conclusion, so the correct answer was likely to make that connection.

Incorrect. This answer weakens the argument by establishing that the comparison used to justify the conclusion isn't relevant to it—if caterpillars can't detect the concentration of pheromones, then one set being heavier than another couldn't be used by the caterpillars to forage.

Incorrect. This answer doesn't address how heavy the route is marked with chemicals, nor does it address future caterpillars following the trails laid out by these caterpillars to find food. At most, it creates a sense that certain trails out of the nest will always eventually lead to food, but it doesn't address the trails from these food sources back to the nest.

Incorrect. This answer doesn't address the use of these trails and the concentration of them on routes to influence future foraging behavior. And if other insects mark routes to food sources with the same pheromones, then the trails could work just as well.

Incorrect. Other species of caterpillars are out of scope, as it doesn't speak to whether the tent caterpillars use the pheromone concentrations to communicate the location of food sources.