LSAT 137 | Section 4 | Logical Reasoning: Q15

LR Question 15 Explanation

QUESTION TEXT: Any good garden compost may appropriately be used for…

QUESTION TYPE: Most Strongly Supported

FACTS:

1. Any good garden compost can help with soil drainage and fertility.
2. The best compost is dark brown, and 40-60% organic matter.
3. Compost with a strong smell of ammonia shouldn’t be used for soil drainage and fertility. Its organic matter hasn’t decomposed.

ANALYSIS: You can draw this question, though it’s not crucial. The first sentence gives us a conditional statement, and so does the third.

Good compost ➞ Drainage (1st sentence)

Drainage ➞ Good compost (contrapositive)

Ammonia ➞ Drainage (3rd sentence)

Ammonia ➞ Drainage ➞ Good compost

(I left out fertility to simplify this. It’s just an extra word that doesn’t affect the logic)

So, any compost that smells of ammonia is not good compost. This is because ammonia compost can’t be used for drainage, and all good composts can be used for drainage.

___________

1. We have no idea why compost with higher than 80% organic matter is not the best. It might not have anything to do with decomposition.
2. 40% organic compost is best, but other compost might still be helpful.
3. There are other reasons compost could be bad. If I laced 50% organic compost with salt, it would be terrible compost, since salt kills plants.
4. This goes too far. The last sentence tells us that organic matter needs to be sufficiently decomposed. But maybe it shouldn’t be completely decomposed.
5. CORRECT. This combines the first and third facts. All good compost can be used for drainage, and ammonia compost can’t be used for drainage. So ammonia compost isn’t good.