Critical Reasoning

I'm going with B because those hunted do not accurately represented the whole deer and elk population. So a higher percentage of deaths in those hunted does not mean it is a valid representation if the weak and diagnosed are being hunted.

OA please. thanks

prachich1987 wrote:Thirty years ago, deer and elk in selected parts of the Rocky Mountains were first discovered with a condition known as wasting disease. In 1970, two percent of the deer and elk killed by hunters were diagnosed with the disease. In 1995, that percentage had grown to six percent. This increase in the incidence of the disease proves that wasting disease has become much more prevalent in the last twenty-five years.

If true, which one of the following selections most seriously weakens the author's conclusion?

(A) Wasting disease has not been discovered in domestic livestock or in moose or bighorn sheep, which are also found in significant numbers in the Rocky Mountains.
(B) Wasting disease tends to make deer and elk lethargic, making them more easily killed by hunters.
(C) Since it was first reported, wasting disease has occasionally been diagnosed in deer outside the Rocky Mountains.
(D) Hunters have grown more reluctant to cooperate with the authorities in reporting their deer and elk harvest, because if wasting disease is diagnosed in their harvest, the meat will be destroyed.
(E) It is very difficult to diagnose wasting disease more than twenty-four hours after death, so many cases of the disease have gone undiagnosed.

OA : after some time

I received a PM asking me to comment.

Premise: Percentage of deer with wasting disease increased from 2% to 6%.
Conclusion: Wasting disease in deer is more prevalent.
Assumption: An increase in percentage = an increase in number.

The easiest way to weaken an argument that uses percentages is to show that the size or composition of the group has changed. The correct answer to the argument above likely will show that the size of the deer population has decreased. If there are fewer deer, then the percentage with wasting disease could have increased (the premise), even though the actual number with wasting disease has declined (invalidating the conclusion). A higher percentage of a smaller number = a smaller result.

Only answer choice B works:
If much of the deer population has been killed by hunters, then the number of deer has decreased. Thus, the percentage with wasting disease could have increased (the premise), even though the actual number with wasting disease has declined (invalidating the conclusion).

The correct answer is B.

D and E each strengthen the conclusion. If hunters are not admitting the number of deer killed (D), or if wasting disease has been going undiagnosed (E), then the percentage of deer with wasting disease could be even higher than has been reported. Thus, both D and E strengthen the conclusion that wasting disease is more prevalent.

@Mitch
But B doesn't say that the disease made these animals lethargic only in 1995.
If the disease makes animals lethargic,then it could had had the same impact even on the animals in 1970.
_____

Hi GmatGuruNY,I can understand why many people think that E strengthens instead of weaken.
I am quoting this from my previous post.

(E) It is very difficult to diagnose wasting disease more than twenty-four hours after death, so many cases of the disease have gone undiagnosed.
In 1970 if there were 10 actual cases of Wast. Dis.
But only 2 were reported
In 1995 if there were 8 actual cases But only 6 were reported
The conclusion incidence of the disease proves that wasting disease has become much more prevalent in the last twenty-five years is Undermined

Dont u think the above scenario is possible too ? I understand a number of scenarios can be imagined wrt a particular choice . But how do we decide which sceniario to consider and which to overlook[/b]

prachich1987 wrote:@Mitch
But B doesn't say that the disease made these animals lethargic only in 1995.
If the disease makes animals lethargic,then it could had had the same impact even on the animals in 1970.
_____

So what? The conclusion is not about why the deer are dying but about whether the disease is more prevalent. If the lethargy started in 1970, then in 1970 it became easier for hunters to kill the deer, reducing the deer population. Given fewer deer, the percentage in 1995 with wasting disease could have increased while the actual number with wasting disease decreased.

mundasingh123 wrote:Hi GmatGuruNY,I can understand why many people think that E strengthens instead of weaken.
I am quoting this from my previous post.

(E) It is very difficult to diagnose wasting disease more than twenty-four hours after death, so many cases of the disease have gone undiagnosed.
In 1970 if there were 10 actual cases of Wast. Dis.
But only 2 were reported
In 1995 if there were 8 actual cases But only 6 were reported
The conclusion incidence of the disease proves that wasting disease has become much more prevalent in the last twenty-five years is Undermined

Dont u think the above scenario is possible too ? I understand a number of scenarios can be imagined wrt a particular choice . But how do we decide which sceniario to consider and which to overlook[/b]

First, an answer choice that could strengthen or weaken the conclusion is not correct. The correct answer choice will clearly weaken the conclusion.

Second, I have a rule: if you have to make up a big story to justify your answer choice, it's probably not right. The justification for B is very straighforward: fewer deer means that a higher percentage with the disease ≠ a higher number with the disease. Look for an answer choice that's easier to justify.

Finally, learn to recognize the common assumptions and understand how to weaken and strengthen each one. As noted above, the easiest way to weaken an argument with percentages is to show that the size or composition of the group changed. If -- before looking at the answer choices above -- you knew that the correct answer likely would discuss a decrease in the deer population, the correct answer (B) would be much easier to spot.

GMATGuruNY wrote:

prachich1987 wrote:Thirty years ago, deer and elk in selected parts of the Rocky Mountains were first discovered with a condition known as wasting disease. In 1970, two percent of the deer and elk killed by hunters were diagnosed with the disease. In 1995, that percentage had grown to six percent. This increase in the incidence of the disease proves that wasting disease has become much more prevalent in the last twenty-five years.

If true, which one of the following selections most seriously weakens the author's conclusion?
(B) Wasting disease tends to make deer and elk lethargic, making them more easily killed by hunters.
OA : after some time

I received a PM asking me to comment.

Premise: Percentage of deer with wasting disease increased from 2% to 6%.
Conclusion: Wasting disease in deer is more prevalent.
Assumption: An increase in percentage = an increase in number.

The easiest way to weaken an argument that uses percentages is to show that the size or composition of the group has changed. The correct answer to the argument above likely will show that the size of the deer population has decreased. If there are fewer deer, then the percentage with wasting disease could have increased (the premise), even though the actual number with wasting disease has declined (invalidating the conclusion). A higher percentage of a smaller number = a smaller result.

Only answer choice B works:
If much of the deer population has been killed by hunters, then the number of deer has decreased. Thus, the percentage with wasting disease could have increased (the premise), even though the actual number with wasting disease has declined (invalidating the conclusion).

The correct answer is B.

Hi GmatGuru,1 last clarification, Here when u say the deer population decreased because the deer have become easier to kill, u mean the deer population was found to have decreased in 1995 because the dear hunting activities prior to 1995 that is 1970-1994

mundasingh123 wrote:

GMATGuruNY wrote:

prachich1987 wrote:Thirty years ago, deer and elk in selected parts of the Rocky Mountains were first discovered with a condition known as wasting disease. In 1970, two percent of the deer and elk killed by hunters were diagnosed with the disease. In 1995, that percentage had grown to six percent. This increase in the incidence of the disease proves that wasting disease has become much more prevalent in the last twenty-five years.

If true, which one of the following selections most seriously weakens the author's conclusion?
(B) Wasting disease tends to make deer and elk lethargic, making them more easily killed by hunters.
OA : after some time

I received a PM asking me to comment.

Premise: Percentage of deer with wasting disease increased from 2% to 6%.
Conclusion: Wasting disease in deer is more prevalent.
Assumption: An increase in percentage = an increase in number.

The easiest way to weaken an argument that uses percentages is to show that the size or composition of the group has changed. The correct answer to the argument above likely will show that the size of the deer population has decreased. If there are fewer deer, then the percentage with wasting disease could have increased (the premise), even though the actual number with wasting disease has declined (invalidating the conclusion). A higher percentage of a smaller number = a smaller result.

Only answer choice B works:
If much of the deer population has been killed by hunters, then the number of deer has decreased. Thus, the percentage with wasting disease could have increased (the premise), even though the actual number with wasting disease has declined (invalidating the conclusion).

The correct answer is B.

Hi GmatGuru,1 last clarification, Here when u say the deer population decreased because the deer have become easier to kill, u mean the deer population was found to have decreased in 1995 because the dear hunting activities prior to 1995 that is 1970-1994

Here's the timeline suggested by answer choice B:

30 years ago: Wasting disease develops in deer.
Result: The deer become lethargic and easier to hunt.
Consequence: The number of deer decreases.
Result in 1995: The percentage with wasting disease goes up, but the actual number with wasting disease goes down (because there are fewer deer).

Does this help?

Thank You GmatGuruNY for the excellent explanations , for making the CR so transparent and direct ,and for giving us a plan of action in case of such problems.You are Great.