In comparing the results of a recent annual spring census to those of

Question

In comparing the results of a recent annual spring census to those of the previous year, biologists observed dramatic changes in the numbers of frogs of two species—Species X and Species Y—and an overall decrease in the combined number of frogs of these species. The biologists hypothesized that this decrease was caused by the unusually cold weather between the two censuses.

Select for A and for B the statements such that the biologists' hypothesis would have the most support if A is true and B is false. Make only two selections, one in each column.

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ID: 700203

Select for  A  and for  B  the statements such that the biologists' hypothesis would have the most support if A is true and B is false. Make only two selections, one in each column.

ID: 700203

MartyMurray · Accepted Answer

In comparing the results of a recent annual spring census to those of the previous year, biologists observed dramatic changes in the numbers of frogs of two species—Species X and Species Y—and an overall decrease in the combined number of frogs of these species. The biologists hypothesized that this decrease was caused by the unusually cold weather between the two censuses.

Select for A and for B the statements such that the biologists' hypothesis would have the most support if A is true and B is false. Make only two selections, one in each column.

Show Spoiler

ID: 700203

The biologists have hypothesized the following:

this decrease was caused by the unusually cold weather between the two censuses

The only information we have about the frogs is the following:

From one spring census to the next there were

- dramatic changes in the numbers of frogs of two species—Species X and Species Y

- an overall decrease in the combined number of frogs of these species

So, we don't know whether the "dramatic changes" involved an increase or decrease in the case of each species, and there's no clear connection between the "unusually cold weather" and the "decrease."

In other words, so far, we have only a correlation between unsually cold weather and an overall decrease, and we know that the biologists have hypothesized that the first caused the second.

Select for A and for B the statements such that the biologists' hypothesis would have the most support if A is true and B is false. Make only two selections, one in each column.

The correct answers can work in a couple of ways.

- A and the negation of B may each on its own confirm the hypothesis.

- Alternatively, A and the negation of B may work together to confirm the hypothesis.

Reviewing the choices, we see the following:
 
 Species X is susceptible to unusually cold weather whereas Species Y is not.

This choice is interesting since it mentions cold weather and provides some confirmation that cold weather could have caused a decrease in the number of frogs of species X.

Species X has a later mating season than does Species Y.

This choice seems irrelevant to the case that the decrease was caused by cold weather.

Both Species X and Species Y are susceptible to similar contaminants.

This choice could possibly weaken the case for believing that the cold weather caused the decrease by indicating that there may have been an alternative cause, "contaminants."

So, negating this choice might strengthen the argument a little.

The number of Species X frogs decreased from the previous spring census.

This choice doesn't make any difference on its own because we already know that there was a decrease, and this choice doesn't indicate what caused the decrease.

The number of Species Y frogs decreased from the previous spring census.

This choice doesn't make any diifference on its own because we already know that there was a decrease, and this choice doesn't indicate what caused the decrease.

So, none of the choices on its own confirms that cold weather caused the decrease. We might get a little confirmation by negating "Both Species X and Species Y are susceptible to similar contaminants," to eliminate an alternative cause, but we don't even know that there were decreases in the number of frogs of both species.

Also, if we choose "Both Species X and Species Y are susceptible to similar contaminants," as the choice to negate, then no other choice would do much to confirm that the decrease was caused by cold weather.  After all, the only choice that mentions cold weather is "Species X is susceptible to unusually cold weather whereas Species Y is not," and that choice is not a very good strengthener since it indicates that one species might possibly have been affected by cold weather while the other would not have been.

So, let's see whether there's a better set of choices since those two aren't a very good set.

Considering the choices carefully, we see the following:

If "Species X is susceptible to unusually cold weather whereas Species Y is not," then cold weather would presumably have caused the number of frogs of species X to decrease but not the number of frogs of species Y.

So, if we negate "The number of Species Y frogs decreased from the previous spring census," to create "The number of Species Y frogs DID NOT decrease from the previous spring census," we have great support for the hypothesis.

After all, in that case, since there was an overall decrease in the number of frogs of the two species, we know for sure that the number of frogs of species X DID decrease.

So,  what we have then is the following:

- There was cold weather and an overall decrease in the number of frogs of two species.

- The number of frogs of Species X, which is affected by cold weather, decreased.

- The number of frogs of Species Y, which is not affected by cold weather, did not decrease.

Accordingly, we have some solid confirmation that the cold weather is what caused the decrease because the decrease in the number of frogs occurred only in the case of the species affect by cold weather.

For  A , select  Species X is susceptible to unusually cold weather whereas Species Y is not.

For  B , select  The number of Species Y frogs decreased from the previous spring census.

KarishmaB · Answer

This is how I would evaluate it:

- biologists observed dramatic changes in the numbers of frogs of two species—Species X and Species Y—and an overall decrease in the combined number of frogs of these species.

Given that overall number decreased but not given whether both X and Y decreased or one decreased etc.

Hypothesis: unusually cold weather between the two censuses

I need to provide support to the hypothesis by giving two statements - 'Statement A' and 'Inverse of Statement B.'
Reading the 5 statements stand alone, I am not sure what to pick. So I come back to statement 1 thinking that perhaps two statements together will make sense.  Species X is susceptible to unusually cold weather whereas Species Y is not. 
It does talk about X being susceptible to cold and hence does support that cold weather could be the culprit. It wil make more sense if we find out that Y did not decrease. Then we know that X decreased a lot and is responsible for most of the reduction in number. We have another statement: The number of Species Y frogs decreased from the previous spring census. 
Inverse of this would be 'number of Y did not decrease'.

Now if we put all this info together, does the hypothesis make more sense?

- Overall number of frogs decreased.
- Speices Y did not decrease (which means that X plunged)
- X is susceptible to cold but Y is not.

It does seem that the unusually cold weather could be the reason for the decrease.

Hence these two statements are the answer.

Iwillget770 · Answer

Hello Experts,

Please help me solve this OG question. I could not understand the requirement of question itself.
Does correct option of A and B should complement each other ?

KarishmaB      @GMATCoachBen

Regards

Sneha2021 · Answer

KarishmaB   MartyMurray

B = Species X is susceptible to unusually cold weather whereas Species Y is not.
A = The number of Species Y frogs decreased from the previous spring census.

Why A can't be #Y decreased and then B would negation (species x is not susceptible and Y is susceptible) - This combination also support the hypothesis.

can you please help to understand why this combination is not possible?
Thanks!

Bismuth83 · Answer

If B were "species X is susceptible to unusually cold weather whereas Species Y is not" then it doesn't necessarily mean the opposite. It could be that species X and Y are both not susceptible. That would mean cold weather didn't affect the frog population, which wouldn't support the hypothesis.

I hope that answered your question!

GauriAkode22 · Answer

OG Answers:

Answer Explanation:

Evaluate

Because the stem asks us to consider the likelihood of something occurring when A is true but B is false, we must consider both selections together.

A and B:

The biologists hypothesized that the decrease in the size between two censuses of the combined population of Species X and Species Y was caused by unusually cold weather between the two censuses. What would support this hypothesis? One possibility would be evidence that both Species X and Species Y are susceptible to unusually cold weather. Notice, however, that this is not one of the options to choose from. The closest option to this is the one stating "Species X is susceptible to unusually cold weather, whereas Species Y is not."'This would support the hypothesis if, but only if, it is not the case that Species Y decreased between the two censuses and did so for some reason other than unusually cold weather. If that were the case, it could be that this other reason is what caused the combined population to decline between the two censuses and not unusually cold weather. Thus, the hypothesis would be supported if it were true that Species X is susceptible to unusually cold weather but Species Y is not while it is false that the number of Species Y frogs decreased fi-om the previous spring census(in other words, the number of Species Y frogs either did not change or increased).

The correct answer for A is Species X is susceptible to unusually cold weather, whereas Species Y is not. The correct answer for B is Be number of Species Y frogs decreased from the previous spring census.

Gourav101 · Answer

Hi Marty, Thanks for your explanation, but doesn't the question state that there was a dramatic change in both X and Y? The answer doesn't provide any confirmation for Y.

cheshire · Answer

We don't have to provide confirmation for that, all the question asks is to select the statements that would support the hypothesis of the biologist. We don't have a lot of information on the overall situation so all we can do is best apply the data we have to the theory given.

bagarwal11 · Answer

MartyMurray 
 KarishmaB

Why can't it be the following way:

1. True:  The number of Species Y frogs decreased from the previous spring census 
 2. False: Species X is susceptible to unusually cold weather whereas Species Y is not.

A lot of times I face challenge in terms of identifying what should come as statement 1 and as statement 2 in conclusion and if-then questions. Can you please help with how to think about this?

MartyMurray · Answer

In answering questions like this one, we have to be careful not to read into answers things they don't actually say or imply.

In this case, I can see why you would choose the statements you mentioned. At the same time, the issue is that, in saying that the second statement is false, we don't know exactly how it's false.

Is all of it false, or just part of it?

If we reverse the entire statement, then it works.

However, if we say that it's only partially false, for instance, by saying that actually both of them are not susceptible to cold weather, then the what we get by saying that the second statement is false doesn't work with the first statement to support the hypothesis.

The issue is pretty subtle, but that's the kind of thing we have to notice.

kartickdey · Answer

KarishmaB

I have one doubt. did the number of species Y increasse? because if Y did not decrease and there is a dramatic change in the number of Y, then I think it must increase.

In comparing the results of a recent annual spring census to those of

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A	B
		Species X is susceptible to unusually cold weather whereas Species Y is not.
		Species X has a later mating season than does Species Y.
		Both Species X and Species Y are susceptible to similar contaminants.
		The number of Species X frogs decreased from the previous spring census.
		The number of Species Y frogs decreased from the previous spring census.

GMAT Two-part Analysis (TPA) Questions

In comparing the results of a recent annual spring census to those of

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