The popular notion that a tree's age can be determined by counting the

Question

The popular notion that a tree's age can be determined by counting the number of internal rings in its trunk is generally true. However, to help regulate the internal temperature of the tree, the outermost layers of wood of the Brazilian ash often peel away when the temperature exceeds 95 degrees Fahrenheit, leaving the tree with fewer rings than it would otherwise have. So only if the temperature in the Brazilian ash's environment never exceeded 95 degrees Fahrenheit, its rings would be a reliable measure of the tree's age.

Which of the following is an assumption on which the argument above depends?

(A) The growth of new rings in a tree is not a function of levels of precipitation.

(B) Only the Brazilian ash loses rings because of excessive heat.

(C) Only one day of temperatures above 95 degrees Fahrenheit is needed to cause the Brazilian ash to lose a ring.

(D) The internal rings of all trees are of uniform thickness.

(E) The number of rings that will be lost when the temperature exceeds 95 degrees Fahrenheit is not predictable

GMATmission · Accepted Answer

IMO E

Bunuel · Answer

OFFICIAL EXPLANATION

The author concludes that one will only be able to determine the age of a Brazilian ash by counting its rings if the temperature in the tree's environment never exceeds 95 degrees Fahrenheit. The author bases this conclusion on the fact that the tree loses rings when the temperature exceeds that level. However, if the number of rings lost by a Brazilian ash at high temperatures could be predicted, then it might be possible to determine the age of a tree even if the temperature exceeds 95 degrees. The author assumes that it is not possible to predict the number of rings lost when the temperature exceeds 95 degrees Fahrenheit.

(A) The argument says nothing about precipitation. This answer choice is out of scope since it would require a number of other assumptions to make it relevant to the argument's conclusion.

(B) Whether other trees share this feature is irrelevant; the argument focuses only on the Brazilian ash.

(C) This choice says that one day of temperatures above 95 degrees = one ring lost. If this is true, then we might actually be able to predict the number of rings lost (if we also know on how many days the temperature exceeded 95 degrees). This hurts the author’s argument; therefore, it cannot be an assumption on which the author depends.

(D) The thickness of the rings is irrelevant.

(E) CORRECT.  The conclusion is that the rings will be a reliable measure only if the temperature never exceeds 95 degrees. This is true only if there is no way to predict how many rings would be lost when the temperature does exceed 95 degrees. (If it were possible to predict this, one might be able to assess the age of a tree using its rings even if the temperature had exceeded 95 degrees.)

mst · Answer

I am somewhere among A, C and E

In E: Probably it does not matter whether we know the the number of rings lost when temperature exceeds 95 degrees. If we knew, say, teh tree loses 1 ring when the temp exceeds 95 degrees. we do not know how many days was the temperature over 95 degrees during the tree's lifetime (since we do not know tree's ag eto begin with)

A: I don't think we are really concerned about how the rings grow. The concern is how the rings can decrease

By POE, C seems to be the choice though it is a little strong because of the usage of  only .

The information in the paragraph says: So if the temperature in the Brazilian ash's environment   never   exceeded 95 degrees Fahrenheit, its rings would be a reliable measure of the tree's age. Usage of never seems to indicate that if the temperature is over 95 degrees on even 1 day, then the tree should at least lose 1 ring.

Phoenix72 · Answer

IMO E,

The number of rings that will be lost when the temperature exceeds 95
degrees Fahrenheit is not predictable- If the count of the rings lost due to high temp was know, then it would be easy to predict the age of the tree.

Clearly E.

bharatg · Answer

Nice explanation from..
https://www.manhattangmat.com/forums/mgm ... t3915.html

Conclusion: “ONLY if the temp in the Brazilian ash’s environment NEVER exceeds 95 degree F will its rings be a RELIABLE measure of the tree’s age.”

If we truly depend on a certain assumption to reach this conclusion, the conclusion should fall apart when we remove or negate the assumption.

Negate (A): The growth of new rings IS a function of precipitation levels.
Result: We could still conclude that the temp needs to stay below 95 degrees in order to use the rings as a measure. Thus, (A) is not an assumption upon which we really rely.

As you note, (A) is an appealing answer: It sure would be nice to know that there are not even more factors affecting the growth of rings. But there is a big difference between a nice-to-know assumption and an assumption-on-which-the-argument-depends. The GMAT always wants the latter!

Negate (E): The number of rings lost when temp exceeds 95 degrees IS predictable.
Result: We can no longer assert that the ONLY way to use the rings to reliably determine age is if the temps stay below 95. You are correct that we would need to know the complete temperature records and number of rings lost as a function of temp, but it would at least be possible to use the rings to determine age. The “only” in the conclusion is really the key word.

sidhu09 · Answer

The central point of the passage is to determine the age of the Brazilian ash trees.

Taking Option E - The number of rings that will be lost when the temperature exceeds 95 degrees Fahrenheit is not predictable

If we negate the above statement, we can rephrase it as follows:

The number of rings that will be lost when the temperature exceeds 95 degrees Fahrenheit is predictable.

Now if in a year, the temperature has exceeded 95 degrees, then we would know the number of rings the tree would lose before hand. If we would like to determine the age of the tree, then all we need to do is add the number of rings lost to the existing rings.

I hope my explanation makes sense. Would love to hear a different version which would help understand the problem in depth.

aniteshgmat1101 · Answer

Pre-thinking:
Conclusion: Number of Rings are reliable only if temperature never exceeds 95F.
Author`s assumption: There is no reliable way to determine tree`s age if temperature exceeds 95F.

After POE got stuck between C and E. So, OA is E in-line with pre-thinking. 
C cannot be the assumption because even the temperature reaches the threshold for 2 days, author`s conclusion is valid.

AryamaDuttaSaikia · Answer

The contention of the author is that since the outermost layers of the wood of the Brazilian Ash peel away at a temperature above 95 degrees Fahrenheit these rings are not a reliable measure of the tree's age. The author assumes that the loss of the rings are not measurable. Only if the loss is unaccounted for then counting the rings to measure the tree's age will not be a reliable technique. Hence the answer is "E".

redfield · Answer

Can someone explain to me how C is also wrong?

Last line of statement "So if the temperature in the Brazilian ash's environment  never exceeded 95 degrees Fahrenheit , its rings would be a reliable measure of the tree's age."

C directly combats the usage of the word "never" in this statement. So the argument assumes that if the environment ever exceeds 95 degrees then it will lose a ring. Answer choice C is essentially this assumption.

The statement also says before this point ""often peel away" not "always", so by it's own admission the final sentence is harsher than the evidence given.

AryamaDuttaSaikia · Answer

"C" gives an additional information. It states another fact. It is not a necessary assumption."Only one day of temperature" also is rather extreme in its tone.

Nevernevergiveup · Answer

The popular notion  that a tree's age can be determined by counting the number of internal rings in its trunk  is generally true. 
However, to help regulate the internal temperature of the tree, the outermost layers of wood of the Brazilian ash often peel away when the temperature exceeds 95 degrees Fahrenheit, leaving the tree with fewer rings than it would otherwise have. So if the temperature in the Brazilian ash's environment never exceeded 95 degrees Fahrenheit, its rings would be a reliable measure of the tree's age.

Which of the following is an assumption on which the argument above depends?
(B) Only the Brazilian ash loses rings because of excessive heat................... we are bothered about this particular tree. It does not matter if others lose rings due to some reason. 
(C) Only one day of temperatures above 95 degrees Fahrenheit is needed to cause the Brazilian ash to lose a ring........ duration of heat exposure need not be assumed.  
(D) The internal rings of all trees are of uniform thickness.................... .thickness is additional information and need not be assumed.

While we can easily eliminate options B, C and D since they are out of scope.
Most of the candidates above(including me) got stuck between A and E.

(A) The growth of new rings in a tree is not a function of levels of precipitation.............. TRAP choice. This seems to indicate that during the scenario of more than 95 degrees Fahrenheit temperature tree only loses rings and does not grow them. This seems to divert us towards reverse causality assumption but there is no reason to assume anything like that regarding growth of new rings.

(E) The number of rings that will be lost when the temperature exceeds 95 degrees Fahrenheit is not predictable
 This may not look as attractive as option A but is the correct answer and can be veified through negation test.
If the number of rings is predictable then we can easily decide the tree age even if in high temperatures and this collapses the argument.

gmatexam439 · Answer

The popular notion that a tree's age can be determined by counting the number of internal rings in its trunk is generally true. However, to help regulate the internal temperature of the tree, the outermost layers of wood of the Brazilian ash often peel away when the temperature exceeds 95 degrees Fahrenheit, leaving the tree with fewer rings than it would otherwise have. So if the temperature in the Brazilian ash's environment never exceeded 95 degrees Fahrenheit, its rings would be a reliable measure of the tree's age.

Which of the following is an assumption on which the argument above depends?
(A) The growth of new rings in a tree is not a function of levels of precipitation. - We are interested in the peeling of rings and not in the growth of the rings. Out of scope. 
(B) Only the Brazilian ash loses rings because of excessive heat. - We are not worried about the other trees. 
(C) Only one day of temperatures above 95 degrees Fahrenheit is needed to cause the Brazilian ash to lose a ring. - If this were the case, then we would be able to identify the age of tree even when the temperature exceeds 95 degrees, since as per the statement "a" ring (only one ring) is lost on a day having temperature greater than 95 degrees. Besides, this is just a fact set stating that the requirement for reduction in tree's rings. Irrelevant or, at best, weakener. 
(D) The internal rings of all trees are of uniform thickness. - Out of scope 
(E) The number of rings that will be lost when the temperature exceeds 95 degrees Fahrenheit is not predictable - Correct. If we can't predict this, then it means that on a day with temperature greater than 95 degree we can't determine the number of rings lost, thus we need a day with temperature less than 95 degree to find out the exact number of rings in the tree.

pbad · Answer

The question misses "Only" in front of if. The question in Manhattan states that the age can be predicted "ONLY if" the temperature doesn't exceed 95 degrees. The assumption being that if temperature exceeds 95 degrees we cannot predict the age. 
E would be the correct answer if the question used "only".
In the current form  the question discusses about a scenario when the temperature DOESN'T exceed 95 degrees so the predictability of age if temperature exceeds 95 degrees has no bearing on the argument.

AnubhavC97 · Answer

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krndatta · Answer

EducationAisle  sir, 
Please evaluate my reasoning.

Option A:- When we negate this option. We get "The growth of new rings is a function of levels of precipitation". Doesn't this weaken our conclusion because the growth is depended on precipitation and not on temperature exceeding 95 degrees Fahrenheit or not. Hence, we would be able to count the new rings.

Option B:- This is irrelevant because why does the Brazilian ash loose a ring is irrelevant.
 
Option C:- This is a weakener because this option tells us that we can count the number of rings when the temperature exceeds 95 degrees.

Option D:- If they are of uniform thickness or not, this doesn't matter. Can we count the rings or not is our concern.

Option E:- This is the correct answer. 
 
Please share your two cents. 
Thanks

EducationAisle · Answer

This looks good Karan!

Good job.

krndatta · Answer

EducationAisle  sir,

Please share your two cents for option A. 
and have a look at my reasoning for option A.

Thanks

Rahilgaur · Answer

(A) The growth of new rings in a tree is not a function of levels of precipitation. -   Irrelevant.

(B) Only the Brazilian ash loses rings because of excessive heat.  Nothing mentioned about any other tree species

(C) Only one day of temperatures above 95 degrees Fahrenheit is needed to cause the Brazilian ash to lose a ring. - One day gives out the relevancy.

(D) The internal rings of all trees are of uniform thickness. - Not required.

(E) The number of rings that will be lost when the temperature exceeds 95 degrees Fahrenheit is not predictable - If we could predict the no. of lost rings due to temp. we could still estimate the age of tree. Hence, Conclusion won't stand relevant anymore. Hence, correct assumption.

VerbalBot · Answer

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The popular notion that a tree's age can be determined by counting the

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