Logical reasoning PrepTest 126 · Section 3 · Question 22

Question prompt

In a study, one Remaining source text redacted.
Why the credited answer is right

Credited answer: A

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument

Valid or Flawed

Flawed

Question Type

Weaken Questions

Stimulus Summary

A study took people who were eating about the same diet and put them into two groups:
Group 1 - High-protein, low-carb diet
Group 2 - High-carb, low-protein diet
Group 1 lost more weight after 10 days than Group 2
Conclusion - The most effective way to lose fat is to eat a lot of protein and few carbs

Answer Anticipation

Wow, there are a lot of elements in this stimulus that we need to analyze for flaws, and a lot of flaws that end up popping up, so let’s get started.
First, we have a study, so we need to consider a sampling flaw, and a correlation/causation flaw.
For the sampling flaw, there’s no indication the study was too small, or that the volunteers were unrepresentative. They started off with a similar diet and were split into two groups, but it doesn’t note that that split was random, so there might be an answer referencing that.
For the correlation/causation flaw, the argument does base a causal conclusion on a correlation - a diet that was correlated with losing weight is concluded to be an effective means of losing weight, so we can look for our standard answers. Identifying an alternative cause is the only one that makes sense. The timeline has the diet happening before the weight loss, so it can’t be reverse causality, and the argument appears to be talking averages, so counterexamples (unless extreme) won’t weaken the argument.
After getting through those flaws, we can see that there is a timeline element to this argument, so we need to consider a timeline flaw. And there is one - they looked at these groups only after 10 days. Maybe the weight loss curve is different for both diets, and the high-protein/low-carb diet is only more effective than the other diet for the first 10 days. The argument would be weakened if the other diet is better over a longer period.
The conclusion is a strong comparison - the diet in question is the “most effective” way to lose body fat. The study only looked at two diets, so it’s too strong to say that the “better” one is the most effective - at most, it could be said that it’s the more effective of the two diets.
Finally, there’s a subtle term shift here. The study monitored the volunteers’s weight, but the conclusion is about body fat. It’s possible that the group that lost more lost water weight, or muscle.
We have a lot of potential answers to juggle, so let’s get to the answers ASAP.

Answer choices

  1. A
    A low–protein, high–carbohydrate diet Remaining source text redacted.
    Why choice A matches the stem
    This answer is related to the last flaw that we noted - the term shift between weight loss and body fat loss. If the group that lost less weight actually lost a lot of body fat but retained water to “hide” that weight loss, then it might be better for body fat loss than the other diet. This answer, therefore, weakens the argument.
  2. B
    Many people who consume Remaining source text redacted.
    Why choice B is not credited
    First, the diet in the argument is a high-protein/low-carb diet, and this answer doesn’t specify that these people are shunning carbs. Second, even if we ignore that, this answer falls into the “counterexample” category, and since the argument is statistical (about averages, not about every single person), a few outliers doesn’t have an impact.
  3. C
    A high–protein, low–carbohydrate diet Remaining source text redacted.
    Why choice C is not credited
    That would mean that not only was body fat lost, but the fat loss must have been rather pronounced since the group on that diet lost more weight overall, and this answer is telling us that they also gained muscle, meaning they must have lost even more fat to account for the weight loss.
  4. D
    In the experiment, the Remaining source text redacted.
    Why choice D is not credited
    This strengthens* the argument - if the high-protein/low-carb lost more weight despite not exercising in a manner that leads to weight loss, then the diet is looking like the cause of the weight loss (this eliminates an alternative cause). Note the asterisk, though - this answer is about weight loss, not fat loss like the conclusion - another reason to eliminate it.
  5. E
    Many of the volunteers Remaining source text redacted.
    Why choice E is not credited
    This answer is trying to play off of the short timeline of the argument. However, without knowing if the low-carb diet is harder to maintain, or that the other diet resulted in persistent weight loss even after returning to a normal diet, this answer doesn’t have an impact on the conclusion.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A Credited 63%
  2. B 18%
  3. C 8%
  4. D 7%
  5. E 3%

Deeper help

Ask follow-ups on any step

Optional AI tutor mode will let you interrogate assumptions, compare answers, and drill weak patterns without leaving the page.

Human-written explanations stay primary; AI is an add-on when you want it.

Discussion

View all discussions Start a discussion