LR Question 10 Explanation
QUESTION TEXT: In a vast ocean region, phosphorus levels have doubled…
QUESTION TYPE: Must be True
FACTS:
Runoff ➞ Phosphorus doubled ➞ plankton ➞ oxygen consumed ➞ few fish survive
ANALYSIS: This question is, in fact, pretty straightforward. It’s a “must be true” question, so you’re not trying to find a flaw in the information.
Instead, you just have to understand the information. I recommend making a diagram like I did above in the “FACTS” section. The stimulus gives you a lot of complex information. If you can reduce it to a short diagram, you can go through the answers more quickly. Everything connects left to right.
___________
- CORRECT. If you look at the diagram in the “FACTS” above, you can see that this is true. Runoff is the first term, and it leads directly to plankton, the third term.
- We can’t say this. We know few fish survive now. But we don’t know how many fish could survive before: maybe only 37% of fish could survive before. That’s more than few, but it’s not most.
- The second sentence says that phosphorus stimulates the growth of plankton. Stimulates just means increases. There could still be some plankton for the bacteria even without runoff.
- Phosphorus levels increased, but that could happen with a constant runoff rate. Runoff flows continously, like water flowing into a bucket. A flow of water at a steady rate will fill a bucket: the rate doesn’t need to increase! Similarly a steady rate of runoff will gradually increase phosphorus levels.
Imagine you pour water into a bucket. You can pour at a constant rate, and the total water level in the bucket will double. Same with phosphorus. Runoff is constantly flowing, and the ocean region is a fixed quantity, like a bucket. - This is waaaaay too broad. We only know about one ocean region. We can’t say if phosphorus produces this impact in every part of the ocean.
More Resources for Must Be True Questions
- Conditional Reasoning Article: Learn about conditional statements on the LSAT.
- LR Diagrams Guide: Learn how to draw LR diagrams.
- Intro to Conditional Reasoning: This intro course lesson covers conditional reasoning basics.
- Intro Course lesson: This intro course lesson covers Must Be True questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers must be true questions.
Hi! I think “proportional” in E is too exact and is not supported. We know the phosphorus levels doubled and oxygen was depleted, but we don’t know if this worked in a proportional way.
I see wrong answers appear with “proportional” or “same” on must be true or necessary questions. For me, they are hard to support due to precision. Have you seen them as correct answers?
Could you explain what “proportional” means on LSAT? Does it mean two elements change at a fixed ratio?
Thanks!
On the LSAT, for one quantity to increase or decrease proportionally to another is for it to increase or decrease at the same rate as that other quantity. So, in this case, for the phosphorous to increase proportionally to the run-off is for it to increase at the same rate as the run-off (i.e. if the run-off doubled in quantity, then the phosphorous would double in quantity.)
You can determine whether a proportional relationship is supported in the same way that you can determine if any kind of inference is supported by a Must be True stimulus — you just need to determine whether that inference adheres to, and in no way contradicts, the letter of the stimulus.
And agreed, we don’t have enough evidence to indicate that there actually is a proportional relationship in this stimulus.