LSAT 147 | Section 4 | Logical Reasoning: Q23

LR Question 23 Explanation

QUESTION TEXT: The diet of Heliothis subjlexa caterpillars consists…

QUESTION TYPE: Must be True

FACTS:

1. Heliothis subflexa caterpillars only eat fruit of the genus Physalis.
2. This fruit has no linolenic acid.
3. Linolenic acid is essential to the growth of many insects, but not of H. subflexa.
4. Volicitin ➞ linolenic acid
5. Most caterpillars have volicitin, but H. subflexa doesn’t.

ANALYSIS: It’s only the final two sentences which matter. You can combine them like this:

Caterpillar (most) ➞ volicitin ➞ linolenic acid

When you add a most statement to a sufficient condition, you can combine the left side of the most statement with the necessary condition. So, we can conclude:

caterpillar (most) ➞ linolenic acid

The rest of the argument was just trying to bog you down in details. When doing a “must be true” question, you should look for statements which can be combined.

___________

1. This is not supported. The argument said that many insects needs linolenic acid for maturation. But that doesn’t mean that they all do, and so H. subflexa might not need it.
2. CORRECT. See the analysis above.
3. This is an incorrect reversal. For volicitin, you need linolenic acid. But the fact that something is necessary doesn’t mean it is sufficient.
4. This is uncertain; we don’t know why H. subflexa only eat Physalis fruits. Maybe those fruits have something essential to H. subflexa, making other food useless. So it’s not poisonous, it’s just unhelpful. (Like eating grass is for us)
5. This isn’t supported. The stimulus says most caterpillars have volicitin (and therefore linolenic acid in their diet), we don’t know how many that refers to. It could only mean 60% of caterpillars, leaving 40% of caterpillars to eat other things. So some other caterpillars could eat only Physalis.