In the arid land along the Colorado River, use of the river's water is

I have chosen A for this question:

The conclusion is: [highlight]If farmers were to remove the trees, more water would be available for crop irrigation.[/highlight]

When I first read the passage, I knew that the question would ask for an answer choice to weaken the argument. If you look at the argument, the reasoning is clearly flawed - just by removing the trees, the author is assuming that the total amount of water available would suddenly increase. There are other factors that the author has not considered - this leads me to my prephrases:

1. The water could migrate elsewhere. For example, maybe the water would move into the voids that the trees have left, or maybe the water would move into other porous spaces.
2. The water may evaporate quicker without the shade of the trees.

Now look at each answer choice:

A. This answer choice looks like one of my prephrases. After careful review of the other choices, this is the answer I chose.

B. The argument has already stated "if farmers were to remove the trees...", so this answer choice already does not make sense because it is assumed in the passage. Also, this answer choice doesn't talk about an increase in the total amount of water, instead it talks about whether the farmers will cut down the trees.

C. This actually supports the argument because it states that these trees constantly have wet roots, so these trees probably consume more water than normal. Therefore, this answer choice is incorrect.

D. We are not concerned about whether the land is prime for farming or not - this answer choice is irrelevant.

E. This answer choice talks about the distribution of the total water, and not about whether the total water will increase or decrease once the trees are removed. Therefore, this answer cannot be correct.

Hi,

Even i fell for D. Its a very good example of the "EGG SHELL GAME" the GMAT loves to play.

The trick is to identify that D - "The strip of land where trees grow along the river’s banks would not be suitable for growing crops if the trees were removed. " limits the argument to only the strip of land near the river

The argument can be weakened to a greater extent if the benefit of having the trees along the river bank could be felt over a larger area. This is clearly seen in A

Hence A is correct

A clearly weaken the conclusion "if farmers were to remove those trees, more water would be available for crop irrigation
"

Please clear my doubt : The trees along the river’s banks shelter it from the sun and wind, thereby greatly reducing the amount of water lost through evaporation : So I concluded from this sentence that if we remove the trees then a great amount of water would be lost through evaporation but in the same case we would have more water for crop irrigation.So let's suppose we have 100 ml of more water available for irrigation and 99 ml is evaporated then also we will have extra 1 ml for growing crops and this 1 ml will be enough to get to our conclusion.I know this is a far fetched conclusion but I want to clear my thought process on this.

What if complete 100ml of water is evaporated then our conclusion is not met!!
If the back end supply of water goes lower, then no more water will be available than what is available today.
This will result in less irrigation and will directly effect farms and crops.

I hope its clear!

narrowed to A and B and picked B (.

I don't get why A is right.. just assumed another scenario and B suited it better. The ARgument says that the farmers have a limited portion of water - let's say 500 Liter per day, if there is more or less water that share would not change; A doesn't say the when we cut all the trees there is almost no water to serve farmers, it just says there is less water.

What's wrong with B - does it strengthen the argument ?

Notice that the "strip of land" talked about in D is just limited to the strip of land along the river's banks where trees grow. This should not be confused with "arid land along the Colorado River", which is really the focus of this question.

So, if D had said "The ARID land where trees grow along the river’s banks would not be suitable for growing crops if the trees were removed", then I believe D definitely would have been the correct answer.

Wow! So easy to get confused on this, during the exam!

Premise: Use of river water is strictly controlled, but there are some trees that use the river's water.
Conclusion: If the trees are removed, more water will be available for irrigation.

We need to weaken this conclusion.
The conclusion can be weakened if we can prove that the trees are not just water suckers, they are actually doing a good job standing there.
Of the given options, option A talks on the same lines by saying that the trees reduce the amount of water that is lost because of evaporation.

Correct Option: A

In the arid land along the Colorado River, use of the river's water is strictly controlled: farms along the river each have a limited allocation that they are allowed to use for irrigation. But the trees that grow in narrow strips along the river’s banks also use its water. Clearly, therefore, if farmers were to remove those trees, more water would be available for crop irrigation

Which of the following, if true, most seriously weakens the argument?

Conclusion - Remove trees -> more water would be available for crop irrigation
To weaken the conclusion , the correct answer will show that there is a problem with the proposed plan .

a. The trees along the river’s banks shelter it from the sun and wind, thereby greatly reducing the amount of water lost through evaporation.
Correct Answer . If the trees greatly reduce the amount of water lost through evaporation , then removing the trees is likely to make LESS water available for crop irrigation . Thus , it will weaken the argument
b. Owners of farms along the river will probably not undertake the expense of cutting down trees along the banks unless they are granted a greater allocation of water in return . Irrelevant .
One should be skeptical of choices that question the difficulty of implementation of the plan .

c. Many of the tree species currently found along the river’s banks are specifically adapted to growing in places where tree roots remain constantly wet.
Incorrect
d. The strip of land where trees grow along the river’s banks would not be suitable for growing crops if the trees were removed.
iSWAT - This option focuses on the strip of land where trees grow along the river bank's .
Also the conclusion focus directly on availability of water .
e. The distribution of water allocations for irrigation is intended to prevent farms father upstream from using water needed by farms father downstream.
Incorrect - Irrelevant

I thought so too, since it says in the premise that farmers have a certain allocation. I thought the allocation would stay the same even if the trees are removed. What is the use of removing the trees if they still don't get any increase in their allocation?

Conclusion: Remove tress - get more water for crops
Premise 1: Arid region water usage is controlled
Premise 2: Famers allocated water

We are looking for an answer that weakens the conclusion that "removing trees will somehow provide farmers with more water to irrigate"

(A). The trees along the river’s banks shelter it from the sun and wind, thereby greatly reducing the amount of water lost through evaporation - Does this weaken the conclusion? To some extent YES, I will keep this as a possible answer because this tells us that the trees are infact not costing the farmers water but saving them water that would have evaporated.

(B). Owners of farms along the river will probably not undertake the expense of cutting down trees along the banks unless they are granted a greater allocation of water in return - Does this weaken the conclusion?NO. We are not concerned with the expense anywhere in this topic. Hence it can be ruled out.

(C). Many of the tree species currently found along the river’s banks are specifically adapted to growing in places where tree roots remain constantly wet - Does this weaken the conclusion? NO. If anything this strengthens the argument that the trees are indeed leeching a lot of water.

(D). The strip of land where trees grow along the river’s banks would not be suitable for growing crops if the trees were removed - Does this weaken the conclusion? NO. We are not concerned with whether or not the soil is cultivable. Don't lose sight of the conclusion that we just need to get more water. Not how we use this water.

(E). The distribution of water allocations for irrigation is intended to prevent farms father upstream from using water needed by farms father downstream - Does this weaken the conclusion? NO. We are not concerned what is the intention behind the allocation. Just whether or not we can get more by removing trees.

Answer A

Question Que: "seriously weaken"
Question Type: weaken, argument

To weaken this type of question:
1. find conclusion 2.find evidence (premise) 3.find assumption (gap) 4. ATTACK the gap (alternate cause)

Conclusion: Farmers cut tree, then more water flow

Evidence: water supply is strictly control: farms along the river have limited access to water for irrigation use.

Assumption (pre-thinking that closes the gap):
Trees are not beneficial in water irrigation. Therefore, if Cut tree, irrigation will improve.

Weaken:
Trees are beneficial in water irrigation. Therefore, if Cut tree, irrigation will get worst

Answer Choice C:
A. Cut tree , water lost through evaporation.

HI Experts can you please clarify why option B

(B) Owners of farms along the river will probably not undertake the expense of cutting down trees along the banks unless they are granted a greater allocation of water in return.

Is incorrect?
Though I know we are not talking about expense here, but this is a Weaken Question and new data can be introduced in options given to us. Plus as question mentioned that use of water is strictly controlled(I assumed by some1 or some agency) so my train of thought was -
FARMER WON'T INVEST IN REMOVING THE TREE IF THAT AUTHORITY GRANTS HIM/HER A GREATER ALLOCATION FIRST

Thanks in advance.
AjiteshArun egmat nightblade354 GMATNinja carcass

We're being asked which choice most weakens the argument, so it's important to read the conclusion of this argument precisely:

If farmers were to remove those trees, more water would be available for crop irrigation.

You're right — we're not talking about the expense of removing trees here, because the conclusion itself states what would happen if farmers remove the those trees.

There is no version of this conclusion where the farmers do not remove the trees. So we're only interested in data that logically connects to the scenario where trees have already been removed.

Choice (A) provides this information by telling us precisely how those trees affect the availability of water. That's why we keep it around as we complete the process of elimination.

Choice (B) never addresses how the presence of trees affects availability of water, so it has no relevance on the specific conclusion we're asked to weaken. In other words, (B) might make perfect sense on its own, but it's addressing a logical conclusion that we weren't asked to weaken. This is why (B) is incorrect.

I hope this helps!

One of the friend asked why not C as answer. Here is my explanation:

Conclusion:
No trees -- > More Water
X --- > Y

Multiple ways of weakening the conclusion .
Z -- > Y
Y -- > X
Even X happens Y may not happen – our A option

Etc.


If X NO Y
It means conclusion is weakened.





If trees remain constantly wet then?
We don’t know what may happen to water availability to farmers.


Say: More water available( because now trees don’t consume more water) –strengthens the claim
But some may say: Because tree roots hold water that’s why water is available. If trees remove , water may not be available. This weakens the claim
So this information in the given option is irrelevant.
Why because you can discuss and argue on either side of the argument: strengthen or weaken. You have no information that can defend or argue against your claim.


If you compare A, you have information in hand that would there would be less water if trees are removed.


Some May think D as attractive answer. Because D kills the problem completely. No crops no discussion of water. But that would be out of scope. Our focus is what happen to water if trees are removed.

HI GMATNinja,

Could you please explain why E is wrong. I had tough time eliminatig it. is it beacuse of the word "intended to"?

The author thinks that removing trees along the banks of the Colorado River is a great idea, because it will result in more water being available for farmers' crops.

We have to weaken this argument. In other words, we have to cast doubt on the idea that removing the trees will result in more water for the farmers.

With that in mind, take another look at (E):

Hmm. This just tells us about who is allowed to use water from the river. It gives no insight at all into how removing the trees will impact the amount of water available to use for irrigation. Will removing the trees be great for farmers, as the author argues, or will it actually have a negative impact on the amount of water available? (E) doesn't help us answer that question at all.

So, (E) doesn't weaken the author's argument. Eliminate (E).

Compare that to (A):

(A) tells us that the trees actually increase the amount of water in the river. So, removing the trees might not be such a great idea -- sure, the farmers won't have to share the water with the trees, as the author says in the passage. However, the farmers might end up worse off if they cut down the trees, because now a bunch of water will evaporate from the river and be unavailable to use for crop irrigation.

(A) gives us a reason to doubt that cutting down the trees will result in more water for crops, so (A) is the correct answer.

I hope that helps!