During and immediately after periods of drought, algae populations in

During and immediately after periods of drought, algae populations in ponds and streams are so severely impacted that populations that rely on algae, such as insect larvae, plummet, and subsequently, so do insect larvae dependent populations, such as minnows, and frogs.
insect larvae rely on algae
minnows and frogs rely on insect larvae
so I think the drought impact is beyond ponds and streams OR the pond population could also contract

RATT question 4 - Seemed easy enough to get to the answer.

Hope I picked the right answer.

A) The impact from drought extends well beyond ponds and streams.
-Nothing told about what impact drought have beyond pond and streams

B) A species’ reliance on rain-dependent populations can lead to its extinction.
- The statement said that the population is impacted, nothing mentioned about extinction.

C) Insect larvae dependent populations impacted by periods of drought revive with subsequent rain.
- Nothing mentioned about subsequent reviving with rain.

D) During periods of drought, the populations of species that depend on pond algae tend to contract.
- Population gets impacted and population tend to contract is analogous in the contest of the statement.

E) If minnows and frogs fail to prosper, it is attributable to a decline in the population of algae in ponds and streams.
- Totally opposite of what the statement says.

A) The impact from drought extends well beyond ponds and streams. Out of Scope

B) A species’ reliance on rain-dependent populations can lead to its extinction. Incorrect
Argument only talks about the populations decreasing and not about extinction.

C) Insect larvae dependent populations impacted by periods of drought revive with subsequent rain. Out of Scope as there is no mention about subsequent rain .

D) During periods of drought, the populations of species that depend on pond algae tend to contract. Correct

E) If minnows and frogs fail to prosper, it is attributable to a decline in the population of algae in ponds and streams.
There might be alternate causes for decline in population of minnows and frogs .

The answer must be option D.

This is an inference type question.

Deconstructing the argument :

Fact 1 : During and after drought the population of algae comes down.

Fact 2 : Population of organisms that rely on algae comes down. Ex of such organisms : insect larvae

Fact 3 : Subsequently , population of organisms that rely on insect larvae comes down.

We have a chain link Fact 1 -> Fact 2 -> Fact 3.

Pre-thinking :

Inference must be something to do with the effect of drought on species dependent on algae .

Sift through the options , only d fits the bill.

Option a : Irrelevant
Option b : OFS
Option c : We do not know if they revive or not , OFS
Option d : Correct
Option e : There could be other factors as well. Not always true.

the passage talks about a chain reaction due to droughts...
All species that dependent on algae are affected..
Hence D is the most proper inference ..

per the meaning D is clearly the inference

In the stimulus it states, severely impacted...D states
During periods of drought, the populations of species that depend on pond algae tend to contract
Keep in mind the time frame....During & immediately..

drought -> algae populations in P&S impacted -> populations dependent on algae i.e. insect larvae plummet -> populations dependent on insect larvae i.e. frogs plummet

D says exactly the same thing

option D can be correctly inferred from the passage.options A,B and C are out of scope options.option E is completely opposite

EMPOWERgmat Official Explanation
Type: Inference
Boil It Down: Rain down -> Algae down -> Larvae down -> Minnows, frogs down
Goal: Based on the prompt, find the option that has to be true with 100% certainty.
Analysis: This is a classic Inference question. Given the information in the prompt that there is this sequence of dependency attributable to rain: Rain down -> Algae down -> Larvae down -> Minnows, frogs down, we need to find an option that follows from that information with 100% certainty.

Bigger GMAT Picture: In Inference questions, GMAC will be guaranteed to deliver 2 types of incorrect options:
❶ Options that seem altogether reasonable, but are not supported by the facts given (this is the most tempting incorrect option variety in Inference questions)
❷ Options that are too extreme to be supported by the facts given



(A) The impact from drought extends well beyond ponds and streams.
Nope! Incorrect Type 1: Very reasonable, but not supported. This option cannot be concluded since on the basis of solely what’s in this prompt, there is no way to know what happens BEYOND ponds and streams.

(B) A species’ reliance on rain-dependent populations can lead to its extinction.
Incorrect Type 2: Too extreme! Outside of the context of this prompt. This option seems completely reasonable, right? But “reasonable” is not the assignment in inference questions. Can you look at this prompt and say “yes, if a species is reliant on rain-dependent populations, that species can go EXTINCT because of that reliance?” No. We are given no basis in the prompt to know that this dependency can lead to the extinction of that species (a decline in population is not even close to the same thing as extinction). It’s the extinction part of the option that gets it into trouble. Extinction is a consequence that’s too extreme on the basis of this prompt.

(C) Insect larvae dependent populations impacted by periods of drought revive with subsequent rain.
Incorrect Types 1, and 2: Very reasonable, but unsupported and too extreme. Since it’s a VERY reasonable supposition to make that if rain returns after periods of drought that insect larvae dependent populations revive with subsequent rain. However, here’s the problem. Do we know that insect larvae populations ALWAYS revive? No. Despite how reasonable that is, the statement that they REVIVE is too extreme since phrasing it as “revive” guarantees revival. Perhaps there are cases in which the populations never revive for whatever reason. Since this option cannot be concluded with 100% certainty, it’s gone.

[b](D) During periods of drought, the populations of species that depend on pond algae tend to contract.
Yes! This has to be true, and there’s one phrase that serves as the primary engine behind why this option wins: “TEND TO”. That phrase “tend to” is so fluffy, lovely, and light that in a prompt filled with absolutes “tend to” makes this option supremely agreeable.

Specifically, here’s the breakdown: on the basis of this prompt, the claim that pond and stream algae dependent species tend to contract can be firmly concluded since we know that algae populations in ponds and streams are so severely impacted that populations that rely on algae plummet (notice that this is phrased as an absolute: populations of algae dependent species plummet), and subsequently so do insect larvae dependent populations (also phrased as an absolute: these populations plummet---that’s what happens, period). That is 100% supported by the prompt. See “EMPOWERgmat Bigger GMAT Perspective” below to learn more about why the phrase “tend to” is so critical here.

(E) If minnows and frogs fail to prosper, it is attributable to a decline in the population of algae in ponds and streams.
Incorrect Type 2: This option attempts an unsupported reversal of logic:
According to the prompt: Algae down causes minnows and frogs to go down
Option E: If the minnow and frog population is down it’s because of algae down
Here’s the problem: do we know for a fact that the only way minnow and frog populations could go down is because of a drop in rain-dependent algae? No. A drop in rain-dependent algae is a factor, but we can’t state that it’s the ONLY factor, so option E is too extreme..



EMPOWERgmat Bigger GMAT Perspective:
The concept of an inference as it appears on the GMAT is widely misunderstood. People often think that Inference questions are asking them to look for something reasonable/generally agreeable, but on the GMAT those are incorrect options. GMAT Inference questions are seeking to measure whether you can determine which option can be factually determined. GMAT Inference questions will directly reward you for that understanding.

Additionally, it’s imperative to know that on the GMAT, we’re asked to operate with the true logical meaning of relative quantity terms such as:
Some - At least 1
Could - Greater than a 0% chance
Might - Greater than a 0% chance
Will - 100% chance
Tend to - At a bare minimum, the phrase “tend to” suggests a greater than 50% chance. The facts in this prompt definitively support at least a 50% chance that during periods of drought, the populations of species that depend on pond algae contract. Note that the phrase “contract” simply means <0, that there is at least some decline.

This is as inference question. so we cannot bring in info in the asnwer chice.

A) The impact from drought extends well beyond ponds and streams. Nothing is mentioned about drought extension

B) A species’ reliance on rain-dependent populations can lead to its extinction. Rain dependent population?

C) Insect larvae dependent populations impacted by periods of drought revive with subsequent rain.Revive?

D) During periods of drought, the populations of species that depend on pond algae tend to contract.Correct. can be easily inferred by from the argument given

E) If minnows and frogs fail to prosper, it is attributable to a decline in the population of algae in ponds and streams. might have some other reason. the above (in the argument) reason is one of the reason. As we know in inference question we cannot bring in new information

A is a good trap b/c
1/ A talks about a general fact, not just the impact of drought on the pond and other species => A is out of scope
2/ A tricks test takers to think that D is incorrect as people will wonder whether the population will decrease or increase.

D is correct.

A is a trap b/c the passage does not tell whether insects or algae-dependent populations are beyond the ponds and streams.

souvik101990 I feel argument is incomplete

I'm confused. Nowhere in the sentence it says that algae population decreases. The only thing that stated is that it changes. Severe means
"of a great degree". Therefore one can assume either decrease or increase of algae and dependent species. If all of them increase in populations, then D is wrong

Isn't D a restatement of what is already given in the passage. How can D be inferred? Shouldn't A be a close second then

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