Logical reasoning PrepTest 107 · Section 3 · Question 9

Incorrect. This answer is about trees that were treated with the new pesticide and didn't see a decrease in insect damage, which cuts against the argument.

Incorrect. This answer is about trees that were treated with both pesticides, and there's no way to disentangle their effects or any effects of the two working together, so we can't use this to strengthen an argument about the effects of just one.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Fruit growers used a new pesticide for 3 years. They lost a smaller percentage of pears. Therefore, at least in the short-term, the new pesticide works better than the old pesticide.

Answer Anticipation:
Let's start with the question stem. This is a Strengthen question, but it specifically asks about a group of trees that didn't show a reduction in losses to insects. Remember this—we'll circle back to it later.

The stimulus discusses a phenomenon—fruit growers used a new pesticide and lost a smaller percentage of their pears to insects. It then concludes an explanation—the new pesticide works! At least in the short term. Phenomenon/Explanation passages generally deal in Correlation/Causation flaws, and this one is no different—the argument is assuming that since the use of the new pesticide coincided with the higher pear yields, it was a cause of those yields.

However, as with all Correlation/Causation flaws, that's a jump—there could have been other causes/explanations for the increased yields that just happened to coincide with the use of the new pesticide. We can strengthen this argument by:
(1) Eliminating an alternative cause
(2) Establishing more examples of cause/effect coinciding
(3) Establishing a control group—orchards that didn't use the new pesticide and didn't see the decrease in proportion of pears lost to insect damage

Circling back to the question stem, it asked us about what group should not show the effect—the reduction in pear losses—in order to strengthen this argument. That falls squarely into the third category—the control group. Let's find an answer, then, saying that it'd strengthen this argument if the effect wasn't seen in orchards that didn't switch to the new pesticide.

Answer Explanation:
If the orchards that used the old pesticide didn't see a decline in damage from insects, then that increases the likelihood that it was, in fact, the new pesticide that caused the observed change instead of something else going on in the district. This answer thus strengthens the argument, so it's the correct answer.

Key Takeaway:
When a question stem provides additional information, be sure to incorporate it into your anticipation and your approach to the answers.

Incorrect. These trees are sufficiently dissimilar from the ones in the district in that they've never been treated with any pesticide. As such, this answer is out of scope.

Incorrect. This answer is about trees treated with the new pesticide that didn't see a decrease in insect damage, which cuts against the argument.