Critical Reasoning

The folktale that claims that a rattlesnakes age can be determined from the no of sections in its rattle is false, but only because the rattles are brittle and and sometimes partially or completely break off. So , if they were not so brittle one could reliably determine a rattlesnakes age simply from the number of sections in its rattle, because one new section is formed each time a rattlesnake molts

which of the following is an assumption the argument requires in order for the conclusion to be properly drawn ?

A) Rattlesnakes molt exactly once a year
B) The rattles of rattlsnakes of different species are identical
C)Rattlesnakes molt more frequently when young than old
D) The brittleness of a rattlesnakes rattle is not correlated with the length of a rattlesnakes life
E) Rattlesnakes molt as often when food is scarce as they do when food is plentiful

Wil post the OA after a few replies !

Number of sections in the rattle --> age of rattle snake

1 new section is formed each time a rattle sname molts.

The missing link in the above statements is the link between the age of the snake and the number of times the molt occurs in a year.

Option A bridges that gap clearly.

IMO - Option A
Official answer please?

Number of sections in the rattle --> age of rattle snake

1 new section is formed each time a rattle sname molts.

The missing link in the above statements is the link between the age of the snake and the number of times the molt occurs in a year.

Option A bridges that gap clearly.

IMO - Option A
Official answer please?

A looks more like a trap . IMO D

(A) is a trap answer. Invert it and you will see why.

"Rattlesnakes do not molt exactly once per year"

This doesn't weaken the conclusion. They could molt twice per year and the conclusion would still follow from the premises.

Now try inverting (E)

"Rattlesnakes do not molt as often when food is scarce..."

The argument states that "if they were not so brittle one could reliably determine a rattlesnakes age simply from...". Put another way this indicates the age is determined only by the number of sections. Thus the inverted version of (E) gives a reason to doubt this conclusion; there is another reason, other than age, that determines the number of sections in a rattle.

Example: take two snakes, the same age, one has had an abundant food supply its entire life and one not. The snake with the abundant food supply will have more sections despite being the same age.

This is the famous "Rattle Snake" problem! One of the most feared in all of LSAT.
Notice I said LSAT, because this is not a GMAT CR question.

LSAT requires you to make clear distinctions between necessary and sufficient assumptions. GMAT CR not so much. Therefore, I'm not convinced that posting necessary assumption questions -- LSAT questions for that matter -- will benefit this forum.

I can be dissuaded

Thanks Luke , Nice explanation !

I did the same mistake as ananth of interpreting " a rattlesnakes age can be determined from the no of sections in its rattle " AS "Rattlesnakes age = No of sections "

Hence, i eliminated E as in that case it would have had infact weakened the conclusion !

OA is E