GMAT Prep RC: Dendrochronology, the study of tree-ring

[RonPurewal]

Well, don't you see a 30 year old man with his hair turning from black to white? That "tree" has different ages!

In a poetic sense, perhaps. In a literal sense, no.

[AbhilashM94]

Okay, for the first question, the passage does nothing at all to suggest that climate conditions are unreliable if only one tree gives us data. In addition, for the second question, the passage is definitely not trying to throw out the whole science of dendrochronology. It seems both of your incorrect answers have the same root cause - you appear to be reading controversy and hostility into the passage where there is none. If you let that go, i would guess that it will become obvious why the correct answers are correct..

Since there was a 'however' in the second para, I too chose B.

But now I see that the second para is tiny in size in comparison to the first, which would take precedence.

If there was a choice that said - explaining how climatic conditions can be deduced from tree-ring patterns & offering a contradiction - that would have been a better choice.

My logic correct?

[RonPurewal]

"Contradiction" is far too strong, and essentially inaccurate. The second paragraph acknowledges some limitations of the tree-ring method, but in no way calls into question the validity of that method as a whole.

• If the choice said "explaining and qualifying...", then, sure.

• Still, it's clear that the primary purpose of the passage is to explain how/why the method works. The second paragraph is basically a "disclaimer", not unlike the medical warnings at the end of drug commercials (whose primary purpose is to sell the drug—not to provide warnings!)

[RonPurewal]

• Also, don't forget that the question is multiple-choice. The other four answers are all fundamentally wrong——as will always be the case (GMAT wrong answers are never "really close to being correct")——so there is no issue.

[gmatkiller_24]

For the 1st question posted by the reader,

The passage suggests which of the following about the ring patterns of two trees that grew in the same area and that were of different, but overlapping, ages?

(A) The rings corresponding to the overlapping years would often exhibit similar patterns.
(B) The rings corresponding to the years in which only one of the trees was alive would not reliably indicate the climate conditions of those years.
(C) The rings corresponding to the overlapping years would exhibit similar patterns only if the trees were of the same species.
(D) The rings corresponding to the overlapping years could not be complacent rings.
(E) The rings corresponding to the overlapping years would provide a more reliable index of dry climate conditions than of wet conditions.

I eliminated all choices but A&C.

I liked A because it kind of was more wishy washy with "often"
And then C kind of took in the info from the last para abt some trees acting differently , but dropped the "often" making it more definite..Hence A is better .

Although i picked C while Answering , Is my reasoning WRT choosing A correct ?

Thanks in advance

I choice B，based on the statement that Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions.

what is wrong in my thinking process?

[RonPurewal]

maybe you're misunderstanding what B says.

B says "if only one of the trees was alive at some point, then we can't trust the climate data at that point."

this is not what the passage says--and it clashes strongly with ordinary common sense (the trees don't interact with each other, so there's no reason why you would need two of them to deduce anything).

[RonPurewal]

... or maybe you're misunderstanding what the passage says.

"Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions."

ok, ron, how would you explain this to a 10-year-old?

• Since the trees were both alive for a while, the patterns from that period should MATCH. We can find the matching parts (= "correlate the patterns").

• One tree was born and died before the other one.

• So we can use the matching parts to combine the two tree patterns into one bigger pattern, which goes from the birth of the older tree all the way to the death of the younger one.

[RonPurewal]

^^ if you understand the above, you'll quickly realize that exactly the opposite of choice B must be true.

our "extended index" incorporates both periods when only one tree was alive (the period before the younger tree was born, and the period after the older one died).
for that to work, we must be able to trust the single-tree data.
which is precisely the opposite of what B says. exact polar opposite. B says white, passage says black.

[RonPurewal]

in other words--if choice B were true, then we wouldn't have an "extended index". we would have an "index" that covered only the overlapping parts of the trees' lives--in other words, an index that's actually shorter than the life of either individual tree.

[gmatkiller_24]

in other words--if choice B were true, then we wouldn't have an "extended index". we would have an "index" that covered only the overlapping parts of the trees' lives--in other words, an index that's actually shorter than the life of either individual tree.

crystally clear!

thanks, Ron.

[RonPurewal]

you're welcome

[das.abhijit34]

Hi Ron,

For the below question I chose C because along with this text "Often, ring patterns of dead trees of different, but overlapping, ages can be correlated to provide an extended index of past climate conditions." I also read "Certain species sometimes add more than one ring in a single year, when growth halts temporarily and then starts again."

This led me to choose C over A. So does that mean for inference questions we can't relate two parts of the passage? This seems a bit uncomfortable to me. Would you be able to point out where my thinking is going wrong?

Thanks you so much in advance!


The passage suggests which of the following
about the ring patterns of two trees that grew in
the same area and that were of different, but
overlapping, ages?
(A) The rings corresponding to the overlapping years
would often exhibit similar patterns.
(B) The rings corresponding to the years in which only
one of the trees was alive would not reliably
indicate the climate conditions of those years.
(C) The rings corresponding to the overlapping years
would exhibit similar patterns only if the trees
were of the same species.
(D) The rings corresponding to the overlapping years
could not be complacent rings.
(E) The rings corresponding to the overlapping years
would provide a more reliable index of

[RonPurewal]

do you know what "only if" means?
"xxxx ONLY IF they're the same species" means that you'll NEVER observe the phenomenon between different species. that's definitely not something you can support with evidence from this passage!

[RonPurewal]

if you continue to have trouble with these kinds of logical qualifier-words, then just make up SIMPLE examples to illustrate their use.

e.g.,
You can enter this club if you have a passport.
(= the same as "If you have a passport, (then) you can enter this club")
—> if you have a passport, you can definitely enter the club.
—> if you don't, you still might be able to enter the club (i.e., there may be other means of entry).

versus
You can enter this club only if you have a passport.
—> if you DON'T have a passport, you CANNOT get into this club. (there's NO OTHER means of entry.)

[das.abhijit34]

Thanks very much Ron! Got it now.

Also, I should have noticed the strong tone of "only if" for an inference question.