LSAT 105 | Section 1 | Logical Reasoning: Q9

LR Question 9 Explanation

QUESTION TEXT: All potatoes naturally contain solanine …

QUESTION TYPE: Sufficient Assumption

CONCLUSION: Peeling wild potatoes makes them at least as safe to eat as unpeeled domesticated potatoes of the same size.

REASONING:

1. All potatoes contain solanine, which is poisonous in large quantities.
2. Domesticated potatoes have very little solanine while many wild potatoes contain poisonous levels of solanine.
3. Most solanine is concentrated in the skin.

ANALYSIS: That seems risky. Just because most of the solanine is in the skin, how do we know peeling the skin makes it safe? Maybe the little that is left in the rest of the potato is still enough to be poisonous.

Let’s illustrate this with some simple numbers. Let’s imagine 2mg is the maximum amount of solanine a potato can have to be safe.

• An unpeeled domesticated potato contains 2mg of solanine (safe).
• An unpeeled wild potato contains 10mg of solanine (poisonous).

For the conclusion to hold, peeling must reduce the solanine in a wild potato to 2mg or less (the same as an unpeeled domesticated potato). So the possible scenarios are:

1. Peeling removes 6mg, leaving 4mg ➞ Still unsafe.
2. Peeling removes 8mg, leaving 2mg ➞ Now safe and as safe as an unpeeled domesticated potato.
3. Peeling removes all 10mg, leaving 0 mg -> Even safer.

The argument only works if peeling reliably reduces solanine to safe levels. Otherwise, we end up in a situation like #1, where the conclusion doesn’t hold. So we need an answer that tells us that a peeled wild potato doesn’t contain more solanine than an unpeeled domesticated one.

___________

1. We already know most solanine is in the skin. Even if wild potatoes have a greater proportion in their skin than the domesticated, this doesn’t guarantee that peeling makes them equally safe.
2. This says the skin of a wild potato alone is poisonous. But we need something that confirms that peeling will actually make it safe.
3. CORRECT. This makes the conclusion logically follow. Peeling wild potatoes makes them at least as safe as their domesticated counterparts.
4. Whether or not there are other poisonous substances isn’t relevant to the comparison of solanine levels.
5. The argument already accounted for this by saying “of the same size”.