In comparing the results of a recent annual spring census to those of the previous year, biologists observed dramatic changes...
GMAT Two Part Analysis : (TPA) Questions
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.
Phase 1: Owning the Dataset
Argument Analysis Table
| Text from Passage | Analysis |
|---|---|
| "biologists observed 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" |
|
| "The biologists hypothesized that this decrease was caused by the unusually cold weather" |
|
Argument Structure
- Observation: Dramatic changes in two frog species with overall decrease
- Hypothesis: Unusually cold weather caused the decrease
- Key Assumption: Cold weather can affect frog populations
- Logical Flow: Observation of decrease → Proposed causal explanation
Phase 2: Question Analysis & Prethinking
Understanding the Question
We need to select statements where:
- A is TRUE: This statement being true should support the cold weather hypothesis
- B is FALSE: This statement being false should support the cold weather hypothesis
The combination of A being true and B being false must provide the most support for the hypothesis.
Prethinking
For the cold weather hypothesis to be strongly supported:
- We'd want evidence showing species affected by cold decreased
- We'd want evidence showing species not affected by cold didn't decrease
- This pattern would directly link the decreases to cold susceptibility
Specific prethinking:
- For A (true): "Cold-susceptible species decreased" or "Species X is vulnerable to cold"
- For B (false): "Cold-resistant species decreased" would be false, meaning they didn't decrease
Phase 3: Answer Choice Evaluation
Evaluating Each Choice
Choice 1: "Species X is susceptible to unusually cold weather whereas Species Y is not."
- Simple meaning: X can be harmed by cold, Y cannot
- For Part A: Strong candidate - establishes differential susceptibility
- For Part B: Not ideal as a false statement
Choice 2: "Species X has a later mating season than does Species Y."
- Simple meaning: X and Y breed at different times
- Doesn't directly relate to cold weather effects
Choice 3: "Both Species X and Species Y are susceptible to similar contaminants."
- Simple meaning: Both species affected by same pollutants
- Introduces alternative explanation (contaminants)
Choice 4: "The number of Species X frogs decreased from the previous spring census."
- Simple meaning: X's population went down
- Could work for A (true) but doesn't explain why
Choice 5: "The number of Species Y frogs decreased from the previous spring census."
- Simple meaning: Y's population went down
- Could work for B (false) - if Y didn't decrease despite cold weather
The Correct Answers
For Part A: Choice 1 - "Species X is susceptible to unusually cold weather whereas Species Y is not."
- Being TRUE, this establishes that cold weather affects species differently
- Directly supports the cold weather hypothesis by providing the mechanism
For Part B: Choice 5 - "The number of Species Y frogs decreased from the previous spring census."
- Being FALSE means Species Y did NOT decrease
- Combined with A, this shows the non-susceptible species (Y) didn't decrease while susceptible species (X) did
- This pattern perfectly aligns with the cold weather hypothesis
Why This Combination Works Best
When A is true and B is false:
- Species X is susceptible to cold → would decrease due to cold weather
- Species Y is not susceptible to cold → would not decrease due to cold weather
- Species Y didn't decrease (B is false) → confirms the pattern
- The overall decrease must come from X's decline alone
- This perfectly supports that cold weather caused the observed changes
Common Traps to Avoid
Choice 4 for A: While "X decreased" being true fits the observation, it doesn't explain WHY X decreased or support the cold weather hypothesis specifically.
Choice 3: Introducing contaminants creates an alternative explanation that would actually weaken support for the cold weather hypothesis.
Choice 2: Mating seasons might relate to cold exposure timing, but it's too indirect compared to direct susceptibility.