prep test 30 section 2 question 22

kevinraney

Can someone explain to me why the answer isn't A

Accounts Playable

Ah, this is one of the more infamous LR questions ever.

This is a necessary assumption question.

The claim that the age of a rattlesnake's age can be calculated from the number of sections on the rattle is wrong. It's wrong because the rattles break-off easily. However, if they were not so easy to break, then one could calculate the age of the rattlesnake from the number of sections since a new section is made every time the rattlesnake molts.

What I am looking for: What does molting have to do with age? Do the rattlesnakes molt at a constant rate? If they didn't, then how would the premise (every time a molt happens) allow us to conclude the age with any accuracy?

Answer A: Be very careful with this one. This is a sufficient assumption, not a necessary assumption. If you negate it, nothing happens to the argument. If rattlesnakes don't molt once a year, then so what? What if they molt 3 times a year? What if they molt one time every 2 years? We simply don't need this. What is needed is something that tells us the molting is at a constant rate. Additionally, the passage only tells us that we can calculate age FROM the sections, not that we simply count the absolute value of the number of sections. If a section forms every 3 years, then we can just multiply the number of sections times 3, and get the age. In other words, this choice is too strong for a necessary assumption.

Answer B: Who cares about appearance? Why can't they look different?

Answer C: This weakens the argument, which is not what we want from a necessary assumption. We want the molting rate to be constant when they are young and constant when they are old. This answer choice does the opposite of what we want.

Answer Who cares about the brittleness? The argument assumes away this problem in its premise.

Answer E: Perfect. This tells us that rattlesnakes molt at a constant rate. No matter the degree of food scarcity, we can be assured that the number of sections can allow us to calculate the age accurately. If this answer choice were not true, then how can we know that the number sections didn't form at different rates when food was scarce or not scarce? Negating this answer choice wrecks the premise/conclusion relationship.

kevinraney

Thank you i see need to study necessary and suffectient assumption questikns a little more