LR Question 15 Explanation
QUESTION TEXT: A person’s dietary consumption of cholesterol and fat is one of the…
QUESTION TYPE: Most Strongly Supported
FACTS:
- Dietary fat and cholesterol affect the level of cholesterol in our blood.
- Blood cholesterol increases as you eat more fat and cholesterol…until you hit a certain level.
- Past that level, dietary fat and cholesterol don’t have much effect.
- Average American fat and cholesterol intake is four times higher than the threshold level.
ANALYSIS: It seems safe to conclude that American blood cholesterol won’t change much due to their fat and cholesterol intake, unless they radically cut consumption. They’re four times above the threshold.
Two of the wrong answers assume you’re not sure what a threshold is. A threshold is a level of something, beyond which an effect occurs.
For example, suppose you have a pool. The top of the pool is a threshold. If you add too much water, it spills over the top. You can change the threshold, perhaps by building a bigger or smaller pool. But you can’t change the threshold by adding water, since water is what the threshold measures.
Using numbers can also help. Suppose the threshold is at 25 units of dietary cholesterol. If you increase dietary cholesterol from 0 to 25, blood cholesterol increases proportionately. But beyond that, if you go from 25 units to 50 or 100, your blood cholesterol only increases a little bit. Likewise, if you go down from 100 units of dietary to cholesterol to 50 units, your blood cholesterol will only slightly decrease. These numbers are helpful for answers B and C.
___________
- This is nonsense. Thresholds, by definition, don’t change based on a change in the thing they measure.
Meaning: maybe you can raise the threshold of fat. Maybe you can eat more fat by exercising more.
But you can’t change the threshold of fat you can eat by eating more or less fat. - Actually, the opposite is supported. American fat and cholesterol consumption is far above the threshold. That means that eating more fat and cholesterol will hardly affect blood cholesterol.
- CORRECT. This is true. Past the threshold, blood cholesterol hardly changes. And even half the typical amount of fat and cholesterol is far above threshold.
- The passage never mentioned non-dietary ways to affect cholesterol. We know nothing about them.
- Actually, diet has the biggest effect when you’re under the threshold.
Recap: The question begins with “A person’s dietary consumption of cholesterol and fat is one of the”. It is a Most Strongly Supported question. Learn how to master LSAT MSS questions on the LSAT Logical Reasoning question types page.
More Resources for Most Strongly Supported Questions
- Intro Course lesson: This intro course lesson covers Most Strongly Supported questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers most strongly supported questions.
I went through the logic of the question in depth. While your explanation in Answer C is partially correct, the answer choice is actually far more robust and the rationale is simpler:
Because the passage does not establish the exact proportional relationship between dietary and serum, any ratio used in answer B will still be supported by the passage. The uncertainty about the specific ratio means that any proportional claim remains valid within the described framework of the passage. This means that the exact value of the fraction (half, one-eighth, etc.) does not change the support for answer B, as the exact proportionality is not defined in the passage.
Thank you for your comment. However, there are some things to clarify. It’s probably easiest with some numbers.
Let’s say the threshold is 25, and the average american diet is 100, 4x the threshold. The passage says:
Up to the threshold (25), dietary and blood cholesterol increase proportionately.
Beyond the threshold, dietary cholesterol only gradually increases blood cholesterol.
100 is well beyond the threshold. So increasing dietary cholesterol will only gradually increase blood cholesterol. This contradicts B.
In C, half of the north american average would be 50. This is still double the threshold, so decreasing dietary cholesterol down to 50 will only gradually increase blood cholesterol. You only see proportional changes if you go below the threshold.
Hope that helps! The issue isn’t the proportionality but rather the different relationship once you pass the threshold.